OK, I've seen tons of confusion over this today. I've personally downgraded my 9.2 3DS, and went through the VERY tedious process of installing the CFW, without owning a GW. Here's everything you need to know.
1. What you need -
3DS or 3DS XL (2DS isn't supported, nor is New 3DS or New 3DS XL) with 9.2 or lower
Any Nintendo DS flashcart that works on your current firmware
Lots of patience
First things first. Go ahead and grab the Gateway 3.0 launcher from somewhere. Place this in the root of your SD card. Now, download the downgrade file appropriate for your region and have this on the root of your SD card. Put the thing in your 3DS. Install the DS mode exploit using any flashcart now.
Now, load the Internet Browser, and go to www.go.gateway-3ds.com to load the exploit. Make sure you clear your cookies, and disable the wireless before launching the internet browser. Re-enable once you have your cookies cleared. Once you're in, dump your current nand and back it up somewhere. This is required to downgrade, so don't back it up before downgrading. After this, run the downgrade app and be patient. You'll now be on 4.2 firmware. From here, backup your nand to your PC. This is very important if you ever want to return to 9.2, or if you have retail eShop stuff you want to keep when you go legit again.
I won't be delving into making a separate emunand in this tutorial. So if you still want to use your retail carts, I can't help you at the moment. Someone surely can point me in the right direction however.
Now for the tedious part. Give all your thanks to Devin, he wrote this, not me. Make sure you use Palentine CFW for this, but other than that, follow this 1:1
Grab the required files from this topic here http://gbatemp.net/threads/4-x-only-cia-cfw-complete-guide.373532/
This should be all you need to get this up and running. A bunch of other stuff I haven't covered, but again, this is the bare basic guide for CFW on 9.2 without a Gateway. Post questions or anything I missed here. Thanks to everyone above.
EDIT: OK, thanks to spinal_cord I've found out you can run a separate emunand on a different SD card on 9.4, allowing you to use this CFW AND stay on the latest firmware to play 7.X and higher games on CFW and access the eShop. What you need for this -
Additional SD card
MT Card 2.3 launcher.dat (here http://www.mt-card.com/index.html)
The Gateway Launcher installed to the DS profile exploit
So, assuming you've already followed the steps here, run the rop multiloader we used earlier to install the Gateway Launcher. Note that you'll need to switch back to the Homebrew Launcher if you want to use the CFW again. Put the MT Card Launcher.dat in the root of your other SD card. Load the DS profile exploit, and the MT Card menu should pop up. Dump your NAND, then format it using the tool in the MT Card menu. From here, launch Classic Mode, then enter the System Settings again. If you're firmware version starts with MT3D, you've done it correctly and can safely update to 9.4 firmware. If not, DO NOT update your system and try again. You'll reboot back into your stock nand after updating. From here, run Classic Mode again and you should be running your emulated 9.4 nand.
1. What you need -
3DS or 3DS XL (2DS isn't supported, nor is New 3DS or New 3DS XL) with 9.2 or lower
Any Nintendo DS flashcart that works on your current firmware
Lots of patience
First things first. Go ahead and grab the Gateway 3.0 launcher from somewhere. Place this in the root of your SD card. Now, download the downgrade file appropriate for your region and have this on the root of your SD card. Put the thing in your 3DS. Install the DS mode exploit using any flashcart now.
Now, load the Internet Browser, and go to www.go.gateway-3ds.com to load the exploit. Make sure you clear your cookies, and disable the wireless before launching the internet browser. Re-enable once you have your cookies cleared. Once you're in, dump your current nand and back it up somewhere. This is required to downgrade, so don't back it up before downgrading. After this, run the downgrade app and be patient. You'll now be on 4.2 firmware. From here, backup your nand to your PC. This is very important if you ever want to return to 9.2, or if you have retail eShop stuff you want to keep when you go legit again.
I won't be delving into making a separate emunand in this tutorial. So if you still want to use your retail carts, I can't help you at the moment. Someone surely can point me in the right direction however.
Now for the tedious part. Give all your thanks to Devin, he wrote this, not me. Make sure you use Palentine CFW for this, but other than that, follow this 1:1
I know I had issues installing the DevMenu so I'm writing this tutorial to show a pretty painless way of installing it.
1. Launch the GW3DS exploit so you're at the GW3DS menu. You want to dump your NAND to the SD card.
2. Backup your NAND.bin file to your PC.
3. Now you'll want to boot into the GW3DS menu again and select "Format emuNAND".
4. Once that's done go to your PC and open the NAND.bin you extracted earlier in HxD. Now here's where things get tricky. You want to copy lines going from offset 00000000 all the way to and including line 000001F0.
5. Once copied go to the beginning of the code. (To the right of where it says 00000000 under offsets.) And click Copy Insert. Once you've done that go ahead and save the NAND.bin file.
6. Almost done. Next put your SD card that you formatted emuNAND on and open up the emuNAND tool made by n1ghty. Click the option to insert emuNAND and insert the NAND.bin file you modified.
7. Now you're going to want to download the files off of GovanifY's website. Throw the files in the 3DS_Stuff folder into the root of your SD card. Extract the rest of it to your Desktop or wherever.
8. Next up you're going to want to get your DS flashcart's microSD card ready, you'll just want to throw thisfile onto it.
Alright so you think you're ready to install the DevMenu? Hope you're ready to reset your 3DS about 50 times.
1. Boot up your DS flashcart and run the NDS file you downloaded. You want to install the Homebrew Rop Loader 4X, (Not the MSETBOSS one. The other one.) Once that's done go ahead and exit to the 3DS main menu.
2. Make sure you have your SD card that you formatted emuNANDon and injected the NAND.bin in the 3DS and go to Settings->Profile->Nintendo DS Profile. Hold L when pressing Nintendo DS Profile.
3. Now your top screen should be blue, and the bottom screen should flash white for a second. If it didn't flash white then you're going to have to restart your 3DS. Keep doing step 2 until it flashes white and your 3DS reboots. (It won't give you an error.)
4. Perfect. Now that your 3DS rebooted and you're in the 3DS' main menu go to your computer. Those files you downloaded from GovanifY's website are going to come in handy. Open run.bat in Notepad and replace "IPTOMODIFY" with your 3DS' IP address. Save run.bat.
5. Now run the run.bat file. If it says it can't connect, keep trying. Eventually it should send a CIA Install command. Congrats. If it doesn't then you'll want to reboot the 3DS, and try again from step 2. (You don't have to keep editing the run.bat file. Once is enough.)
6. If it worked, turn off the 3DS. Turn it back on and do the Settings->Profile->Nintendo DS Profile exploit again except don't hold L. It make take you a few tries like it did before until the 3DS actually reboots into the menu.
7. You should see a gift box on your 3DS' main screen. If not then you might need to download something from the eShop. Which requires you to be on the latest emuNAND, connect to the eShop, download a demo, and then reinjecting your modified NAND.bin file into the SD card. (I had a backup of my SD card with demos from the eShop so I just copied that over to the SD card.) Congrats.
Grab the required files from this topic here http://gbatemp.net/threads/4-x-only-cia-cfw-complete-guide.373532/
This should be all you need to get this up and running. A bunch of other stuff I haven't covered, but again, this is the bare basic guide for CFW on 9.2 without a Gateway. Post questions or anything I missed here. Thanks to everyone above.
EDIT: OK, thanks to spinal_cord I've found out you can run a separate emunand on a different SD card on 9.4, allowing you to use this CFW AND stay on the latest firmware to play 7.X and higher games on CFW and access the eShop. What you need for this -
Additional SD card
MT Card 2.3 launcher.dat (here http://www.mt-card.com/index.html)
The Gateway Launcher installed to the DS profile exploit
So, assuming you've already followed the steps here, run the rop multiloader we used earlier to install the Gateway Launcher. Note that you'll need to switch back to the Homebrew Launcher if you want to use the CFW again. Put the MT Card Launcher.dat in the root of your other SD card. Load the DS profile exploit, and the MT Card menu should pop up. Dump your NAND, then format it using the tool in the MT Card menu. From here, launch Classic Mode, then enter the System Settings again. If you're firmware version starts with MT3D, you've done it correctly and can safely update to 9.4 firmware. If not, DO NOT update your system and try again. You'll reboot back into your stock nand after updating. From here, run Classic Mode again and you should be running your emulated 9.4 nand.