What you will need:

- 64-bit OS
- A decrypted .3ds file of the game you want to mod
- The mod you want to install
- 3DS to CIA by Katsu (python 2.7 required)
- 3dstool
- Citra 3DS Emulator (you won't need it to do the hacking, only to run the game afterwards)

How to install the mod:

0. Before you start, if you don't already have it, download Python 2.7 with the link provided and install it; also, if you use Windows you must add Python to the PATH Environmental Variable. (To check whether you need to do this last bit, type python in the command prompt and hit Enter: if you get the message ‘python’ is not recognized as an internal or external command, you need to add Python to PATH.)

<!> Since many people are asking me about Fire Emblem Fates, namely adding the Same-sex Marriage patch by @UnassumingVenusaur, I'll use it as an example.

1. Rename your .3ds to <filename_modified.3ds>. Extract the archives of both 3DS to CIA and 3dstool

2. Drag and drop your .3ds on Make2.07.bat in the 3DS to CIA folder you've previously extracted.

Wait until you get this window:

4. Leaving this command prompt (3ds_to_cia_2.07) open so you can later rebuild the game, go to the folder where the files have been extracted (don't move or delete the .3ds file which has been moved there) and copy the romfs file to the 3dstool directory which you've previously extracted.

5. To extract the romfs file, use the following command:

3dstool -xvtf romfs romfs.bin --romfs-dir romfs

If you're not familiar with using the command prompt, here is a quick walkthrough:

+++++++

To open the command prompt, go to Start and type "cmd" and open the program that comes up.

You'll get a black window. Type this in (including the first space): cd "path to the 3dstool folder on your computer goes here"
Hit Enter, and you should get a string with the path to the 3dstool folder.
For instance, on my pc, I type:

C:\Users\Username> cd "C:\Giochi\Nintendo3DS\3ds hacking tools\3dstool"

And I get:

C:\Giochi\Nintendo3DS\3ds hacking tools\3dstool>

To extract the romfs file, use the command:

3dstool -xvtf romfs romfs.bin --romfs-dir romfs

Following the example above, it'll look like this:

To use the command, after you've copy-pasted 3dstool -xvtf romfs romfs.bin --romfs-dir romfs, hit Enter.
Wait until 3dstool is done extracting the romfs.bin file. You'll know when it stops and the same string with the path to the 3dstool folder appears.

+++++++

6. Keeping the console open so you can later rebuild the romfs file, delete the file you've extracted and go to the folder which contains the extracted files.

7. Depending on the mod, you'll now have to follow the instructions provided by the modder themselves, but generally you'll have to copy and paste the files provided by the modder (usually replacing the original ones). Modders often provide different folders for HANS, Luma and NTR CFW but the files inside are the same. Just use the HANS ones if you don't know which ones to choose, and remember to use the ones for your region (USA/EUR/JP)!

In the case of FEF, copy the contents of the HANS version>Your region folder, and paste them in the romfs folder:

8. Having applied the mod/hack, go back to the command prompt and use the following command to rebuild the romfs file:

3dstool -cvtf romfs romfs.bin --romfs-dir romfs

9. Replace the modified romfs file with the one in the extracted folder.

10. Go back to the 3ds_to_cia_2.07 window from step 3, press 6 (Rebuild 3DS) and then s to start

Wait until the rebuilding is done. (The process is pretty long and heavy, you likely won't be able to do anything else in the meantime.)

You should get two folders with your original file and the modded one respectively. Done!

POSSIBLE ERRORS

An issue people who use Windows 10 have run into is the batch file (3ds to cia; step 2) not running at all (opening and closing right after). This may be caused by encoding.
If you've got notepad++ (or if you don't, you can find it among the 3ds to cia "tools": 3ds_to_cia_v2.07\tools\n++), you can open the batch file for editing with it and check "Encoding". If anything else besides UTF-8 (or ANSI) is selected, you should select UTF-8 (without BOM) and save the file.

Most errors occur when rebuilding the .3ds file (step 10), and they're mostly related to the rsfgen.py script and Python by extension.

If you get this error up here, it means you have Python 3.5 installed, and it's being used to run the script instead of Python 2.7

Other instances:
- You don't have Python installed
- Python is installed in a partition where the system can't find it: install python in the same partition where your OS is!
- [Windows] Python's directory hasn't been added to the PATH e.v. (see Step 0)
- Python is not selected as the program to open .py files. If this happens, Pythonw.exe might have been selected to open .py files, while it should be Python.exe. In this case a white window with the script will appear, and once you close it, you'll get the fateful ERROR. You'll have to change the default program to open .py files to the correct one.

(If you see this the default program used to open .py files is pythonw.exe, you need to change it to python.exe)

In case you experience any other issues, tell me and I'll help you out!

-------

If you have any questions, feel free to ask!

Credits go to the creators of Citra, 3DS to CIA and 3dstool. Thank you!

 

[toblyoko]

Hello, first I would like to say thank you so much for the tutorial. I used it to install the same mod for Awakening and it worked just fine. However, today I have been trying to install the same mod you are installing for Fates in the tutorial with a bit of trouble. I've followed the tutorial step by step and done just about everything. Everytime it turns out just fine, but when I try to open the game in citra, it says that citra has stopped working. It doesn't just stop responding, it says it stops working and the only option is to close the program. The starts just fine before installing the mod, but once I install the mod, this error occurs everytime. At first I thought it was because I had installed DLC before installing the mod, but I redid this process with a clean copy of Fates and the problem still occurs. I do not know what to do.

Okay, I tried a different method of installing the mod and it seems to be working now. Thank you though. Please ignore this.

 

[Foee]

Hello, I'm running into the same problem as Takimei was, when I drag the .3ds into the batch file it just closes and does nothing. Running it as admin and dragging the .3ds file doesn't cause it to close, but still nothing happens, and it closes as soon as I touch any key. The encoding is UTF-8, and python shows up as working fine when I test it in cmd. Any ideas? Thank you.

 

[FriendlyHacker]

Hello, I'm running into the same problem as Takimei was, when I drag the .3ds into the batch file it just closes and does nothing. Running it as admin and dragging the .3ds file doesn't cause it to close, but still nothing happens, and it closes as soon as I touch any key. The encoding is UTF-8, and python shows up as working fine when I test it in cmd. Any ideas? Thank you.View attachment 169306

Hi there! I'm sorry you're having issues. Can I ask what your OS is?

 

[Foee]

Hi there! I'm sorry you're having issues. Can I ask what your OS is?

I'm using Windows 10

 

[FPSPro]

First of all, I would like to thank you for this great tutorial!
Everything is well explained and it's easy to follow your step-by-step guide. Awesome work!

Unfortunately, after following your steps, the created ROM at the end isn't working in Citra. When I try to start the game, citra is loading a few seconds and then it's closing itself. Beside that problem, there was no error coming up during the process. So I'm not sure, what the problem actually is. I also tried other methods (like using Karameru and HackingToolkit9Ds) but they didn't work at all, especially HackingToolkit9Ds because of my already decrypted ROM.

Do you have an idea, what I could do?
I just tried to replace some bcstm-files in Animal Crossing New Leaf with and I used a decrypted ROM.

Otherwise, thanks again for your tutorial and have a nice day!

 

[FriendlyHacker]

First of all, I would like to thank you for this great tutorial!
Everything is well explained and it's easy to follow your step-by-step guide. Awesome work!

Unfortunately, after following your steps, the created ROM at the end isn't working in Citra. When I try to start the game, citra is loading a few seconds and then it's closing itself. Beside that problem, there was no error coming up during the process. So I'm not sure, what the problem actually is. I also tried other methods (like using Karameru and HackingToolkit9Ds) but they didn't work at all, especially HackingToolkit9Ds because of my already decrypted ROM.

Do you have an idea, what I could do?
I just tried to replace some bcstm-files in Animal Crossing New Leaf with and I used a decrypted ROM.

Otherwise, thanks again for your tutorial and have a nice day!

Hi there! Thank you very much for trying my method and for the kind words!
Using an already decrypted ROM shouldn't be a problem when hacking, as long as it runs on Citra before you do any modding. The 3ds to cia batch would have come up with an error (as it often does), so I'd say the problem isn't there, either.
Could you please tell me what files you changed, and what those changes are supposed to do? Some games are finicky when it comes to changing some particular files; though if it's something that has worked for someone else, that would rule out this possibility.
There is also another method you could try, described by @Fishmalk here (step 1 to 3 and 5)!

 

[FPSPro]

Hi there! Thank you very much for trying my method and for the kind words!
Using an already decrypted ROM shouldn't be a problem when hacking, as long as it runs on Citra before you do any modding. The 3ds to cia batch would have come up with an error (as it often does), so I'd say the problem isn't there, either.
Could you please tell me what files you changed, and what those changes are supposed to do? Some games are finicky when it comes to changing some particular files; though if it's something that has worked for someone else, that would rule out this possibility.
There is also another method you could try, described by @Fishmalk here (step 1 to 3 and 5)!

Hello there!
Thanks for your quick response, I just tried the method you mentioned from Fishmalk and it's finally working! I'm so glad about that. Now I can enjoy the nostalgia of the good old Animal Crossing Music. Thanks a lot!


It's a good question, why the method with the "3DS to CIA" and "3Dstool" wasn't working for me. Before I even replaced some music files in the romfs-folder, I followed your guide and tried to create a .3ds file without any changes. And this file wasn't working for Citra too, so I think, that the problem occurs somewhere else. I'm also not sure if the problem comes with the decryption because, as you already mentioned, the whole process was working fine without any problems.
Actually, I just wanted to replace some .bcstm music files, but since the problem existed before editing these, it must be something else...


But anyway: It's working now with your help. I hope that many other people will find a solution for their problem in your thread.
I wish you all the best and continuing success with all your projects! Thanks a bunch!

 

[FriendlyHacker]

Hello there!
Thanks for your quick response, I just tried the method you mentioned from Fishmalk and it's finally working! I'm so glad about that. Now I can enjoy the nostalgia of the good old Animal Crossing Music. Thanks a lot!


It's a good question, why the method with the "3DS to CIA" and "3Dstool" wasn't working for me. Before I even replaced some music files in the romfs-folder, I followed your guide and tried to create a .3ds file without any changes. And this file wasn't working for Citra too, so I think, that the problem occurs somewhere else. I'm also not sure if the problem comes with the decryption because, as you already mentioned, the whole process was working fine without any problems.
Actually, I just wanted to replace some .bcstm music files, but since the problem existed before editing these, it must be something else...


But anyway: It's working now with your help. I hope that many other people will find a solution for their problem in your thread.
I wish you all the best and continuing success with all your projects! Thanks a bunch!

You're welcome! I'm sorry this method didn't work for you, but I'm glad you managed to make it work with the other one!
Thank you for your kind words, I wish you all the best, too!

 

[Xilthz]

I've been trying to modify the romfs, but when I repack it w/ katsu's application, I have rsf error
[rsf error] error processing rsf file
Installed python27 on C: and I have no other python version. I've followed these steps but it keeps saying rsf error like above. I'm not good with rsf editing, but...
3ds have been already decrypted(and tested to citra and it runs) and I just want to edit the music but it keeps saying rsf error when rebuilding 3ds + orig. exheader.
Any ideas why this happened ?

Rn I'm trying to extract romfs through katsu's program and it still in the process saving the romfs after editing.
EDIT:
Okay, extracting through katsu's program deletes everything and it gives rsf error.
Idk how rsf work and which one makes it error

Update:
I tried to fiddling a bit on rsf and see the rsf on my end, the company code and product code isn't human language so I changed that by following the exheader.txt or info.txt from those extraction, it work. Didnt crash but, citra seems to stuck on black screen when I started it. Turns to .cia though. Do I need to convert it to 3ds ?

 

[FriendlyHacker]

I've been trying to modify the romfs, but when I repack it w/ katsu's application, I have rsf error
[rsf error] error processing rsf file
Installed python27 on C: and I have no other python version. I've followed these steps but it keeps saying rsf error like above. I'm not good with rsf editing, but...
3ds have been already decrypted(and tested to citra and it runs) and I just want to edit the music but it keeps saying rsf error when rebuilding 3ds + orig. exheader.
Any ideas why this happened ?

Rn I'm trying to extract romfs through katsu's program and it still in the process saving the romfs after editing.
EDIT:
Okay, extracting through katsu's program deletes everything and it gives rsf error.
Idk how rsf work and which one makes it error

Update:
I tried to fiddling a bit on rsf and see the rsf on my end, the company code and product code isn't human language so I changed that by following the exheader.txt or info.txt from those extraction, it work. Didnt crash but, citra seems to stuck on black screen when I started it. Turns to .cia though. Do I need to convert it to 3ds ?

Hi!
If you need to change something in the .rsf file before the batch starts rebuilding the .3ds, you can follow the same steps in this guide, except that at step 10 you press both 6 & 8, and when the .rsf is opened, you can change whatever needs to be changed. I had issues with python (I needed the 3.5 version) so I also check my .rsf files before rebuilding now...
Btw, did you add Python to PATH?

 

[Xilthz]

Hi!
If you need to change something in the .rsf file before the batch starts rebuilding the .3ds, you can follow the same steps in this guide, exept that at step 10 you press both 6 & 8, and when the .rsf is opened, you can change whatever needs to be changed. I had issues with python (I needed the 3.5 version) so I also check my .rsf files before rebuilding now...
Btw, did you add Python to PATH?

I did. Advanced System has that "C:\Python27" on their Environment Variables. I put it on the very bottom of everything else that has existed.
I have already made sure it's Python27.
Do I need python 3.5 version now ? I probably misunderstood this whole thread

Anyway, when I first repack, change the music file(just a couple, not every music were changed), it gives me rsf error. I checked the rsf file w/ n++, the company code says : <+ and product code says... well not human-language. There are letters/numbers but theres few black square between them and some symbols. I changed company code to 01 and product code to CTR-A2BA
The repack is successful, but when launching the game through citra, it just black screen. Console of citra also doesnt give more text after it says
"Service.SRV <Warning> core/hle/service/sm/srv.cpp:RegisterClient:49: (STUBBED) called"
It's complete black screen and the console(citra) stopped there. It's like the game hanged but citra is still running.

(Altho that file turns to be .cia, idk, probably I tried romfs extraction through katsu's. But I have to try 3ds extraction, change the music, use auto rsf, then rebuild 3ds yet have to go another hour.).

 

[FriendlyHacker]

I did. Advanced System has that "C:\Python27" on their Environment Variables. I put it on the very bottom of everything else that has existed.
I have already made sure it's Python27.
Do I need python 3.5 version now ? I probably misunderstood this whole thread

Anyway, when I first repack, change the music file(just a couple, not every music were changed), it gives me rsf error. I checked the rsf file w/ n++, the company code says : <+ and product code says... well not human-language. There are letters/numbers but theres few black square between them and some symbols. I changed company code to 01 and product code to CTR-A2BA
The repack is successful, but when launching the game through citra, it just black screen. Console of citra also doesnt give more text after it says
"Service.SRV <Warning> core/hle/service/sm/srv.cpp:RegisterClient:49: (STUBBED) called"
It's complete black screen and the console(citra) stopped there. It's like the game hanged but citra is still running.

(Altho that file turns to be .cia, idk, probably I tried romfs extraction through katsu's. But I have to try 3ds extraction, change the music, use auto rsf, then rebuild 3ds yet have to go another hour.).

Ah, no no, you don't need Python 3.5 and actually don't install it ever if you want to do romhacking with this method and you don't need the 3.5 version for something else, otherwise it'll be a hassle to force the system to use 2.7, even after you uninstall 3.5...
Does the .3ds file work on Citra before you do any modding?
But I think the issue is the fact that you extracted the romfs with katsu's batch (if I understood correctly) and changed it to .cia. If you use katsu's batch to extract the romfs it messes with non unicode characters in filenames and within the files.
If you don't want to use this method because it's too long and complicated (which is totally understandable) you can also try Fishmalk's method, it's quicker and it should work (scroll up a bit in this thread to find the link).

 

[Xilthz]

Ah, no no, you don't need Python 3.5 and actually don't install it ever if you want to do romhacking with this method and you don't need the 3.5 version for something else, otherwise it'll be a hassle to force the system to use 2.7, even after you uninstall 3.5...
Does the .3ds file work on Citra before you do any modding?
But I think the issue is the fact that you extracted the romfs with katsu's batch (if I understood correctly) and changed it to .cia. If you use katsu's batch to extract the romfs it messes with non unicode characters in filenames and within the files.
If you don't want to use this method because it's too long and complicated (which is totally understandable) you can also try Fishmalk's method, it's quicker and it should work (scroll up a bit in this thread to find the link).

It works before modding. And I found this tutorial is easier to read and to look at then fishmalk's(no offense however) but I'll try his method later.
I haven't installed python 3.5 yet. Just 2.7 and I sort of placed it on program files(x86) earlier but I reinstalled it to C:\ instead the x86 files.
And I just tested the 3ds extraction, pasted the edited romfs.bin and start to rebuild .3ds. And it gives me .rsf error. I had a hunch I have to edit the .rsf file, but even I did earlier, it hanged on citra for no reason. Console didnt even tell any error. Just stopped on the warning I mentioned earlier.


Btw, the .rsf file on n++ looked like this
(ignored the "text" in the pokemonultramoon_modified.txt. For some reason, gbatemp doesn't allow me to post the .rsf codes)

 

[FriendlyHacker]

It works before modding. And I found this tutorial is easier to read and to look at then fishmalk's(no offense however) but I'll try his method later.
I haven't installed python 3.5 yet. Just 2.7 and I sort of placed it on program files(x86) earlier but I reinstalled it to C:\ instead the x86 files.
And I just tested the 3ds extraction, pasted the edited romfs.bin and start to rebuild .3ds. And it gives me .rsf error. I had a hunch I have to edit the .rsf file, but even I did earlier, it hanged on citra for no reason. Console didnt even tell any error. Just stopped on the warning I mentioned earlier.


Btw, the .rsf file on n++ looked like this
(ignored the "text" in the pokemonultramoon_modified.txt. For some reason, gbatemp doesn't allow me to post the .rsf codes)

Hmm, ok, that .rsf doesn't look bad besides those two gibberish spots, so you can just change them when you get to step 10.
You should keep Python27 in the path that you added to the PATH environmental variables, otherwise the system won't be able to find it.
I'm pretty sure you get a black screen on citra because you used the batch to extract the romfs and edit it. Try using 3dstool to do that instead, so you can be sure that the romfs isn't the issue. Then do the rebuilding by pressing 6 & 8 and change those bits that don't look quite right in the .rsf
If it still doesn't work I can guide you through Fishmalk's method, instead.

 

[Xilthz]

Hmm, ok, that .rsf doesn't look bad besides those two gibberish spots, so you can just change them when you get to step 10.
You should keep Python27 in the path that you added to the PATH environmental variables, otherwise the system won't be able to find it.
I'm pretty sure you get a black screen on citra because you used the batch to extract the romfs and edit it. Try using 3dstool to do that instead, so you can be sure that the romfs isn't the issue. Then do the rebuilding by pressing 6 & 8 and change those bits that don't look quite right in the .rsf
If it still doesn't work I can guide you through Fishmalk's method, instead.

Okay, so I need to edit the .rsf file, more importantly in Company and Product Code to 01 and CTR-A2BA right? Just that and nothing else needed to be added, removed or changed ?

 

[FriendlyHacker]

Okay, so I need to edit the .rsf file, more importantly in Company and Product Code to 01 and CTR-A2BA right? Just that and nothing else needed to be added, removed or changed ?

Nope, everything else was grabbed by the rsfgen.py script properly, it seems. And actually, I'd say those parts shouldn't cause problems, either, but to be sure, you can change them. I'm sure the black screen problem is caused by the romfs.bin: it must have been corrupted by ctrtool, which is the tool used by the batch for some reason. ctrtool is perfectly fine for non-japanese games, but it will corrupt games that were made in Japan.

 

[Xilthz]

Nope, everything else was grabbed by the rsfgen.py script properly, it seems. And actually, I'd say those parts shouldn't cause problems, either, but to be sure, you can change them. I'm sure the black screen problem is caused by the romfs.bin: it must have been corrupted by ctrtool, which is the tool used by the batch for some reason. ctrtool is perfectly fine for non-japanese games, but it will corrupt games that were made in Japan.

Okay, I'll give it a shot. I'll tell ya here when work or probably theres an error that I don't understand
Thanks

--------------------- MERGED ---------------------------

Okay, so I did w/ 3dstool, the .rsf error is still not resolved.
EDIT:
And tbh, this is actually for my friend. He wants to change the music but doesnt know anything how so he asked me.
He only gave me a usb and the file is in there named "Pokemon Ultra Moon.3ds"
It just that w/ said folder. Is that fine if you only have the .3ds but it has been decrypted already?

 

[FriendlyHacker]

Okay, I'll give it a shot. I'll tell ya here when work or probably theres an error that I don't understand
Thanks

--------------------- MERGED ---------------------------

Okay, so I did w/ 3dstool, the .rsf error is still not resolved.
EDIT:
And tbh, this is actually for my friend. He wants to change the music but doesnt know anything how so he asked me.
He only gave me a usb and the file is in there named "Pokemon Ultra Moon.3ds"
It just that w/ said folder. Is that fine if you only have the .3ds but it has been decrypted already?

Also press 8 before rebuilding, so that the .rsf file comes up and you can modify it.

 

[Xilthz]

Also press 8 before rebuilding, so that the .rsf file comes up and you can modify it.

Okay, so I did editing rsf file, it worked when I only changed the company code and product code. No .rsf errors. The problem now is though...

Citra crash when loading the game.
No errors, no anything.

Probably my nvidia gpu is outdated. I'll check it on later

 

[FriendlyHacker]

Okay, so I did editing rsf file, it worked when I only changed the company code and product code. The problem now is though...

Citra crash when loading the game.
No errors, no anything.

Wow, I'm sorry you're experiencing so many problems...
You know, I think you should try .Net 3ds Toolkit, instead. It's easier, it could work just fine and you won't have to be stressed by all these errors. You can download the latest version here, it has a GUI and it's pretty straightforward to use.