But there is a repacker,
see the post for it here. As for the extractor,
that post is here.
That might be a little tricky. You
might be able to use a similar process I will explain for the PAPA files. More on that later.
I'll try my best to explain this, but I recommend you read through
this thread on Reddit where I was figuring out how to do this.
So basically, you start with the xbb unpacker you should already have from Xentax. This will leave you with many files. Acquire a program called EditPad Pro, pick a random PAPA file to edit, make a backup of it (you'll need it for later), and open it in EditPad Pro. Notice it displays in hex by default. Find the tab for this file on the top-left, right click>Hexadecimal>Off (text file). You are now viewing the file as a text document. Notice there are still null bits inbetween each character.
In the menu at the top, navigate to Convert>Text Encoding. Notice that the encoding is currently "Windows 1252: Western European." Change it to "Unicode,
UTF-16 Little Endian."
You will now see that all the text in the PAPA file (I'm using one from Msg.xbb in this example) is easily readable and searchable - no more spaces inbetween characters. At this time, make your changes to the file. Add text, remove text, do whatever. Just be careful you don't remove any special characters before each MES tag (they look like Japanese symbols), as these are used to properly format the text in-game. Once you've made your changes, go back to Convert>Text Encoding, and change the encoding back to Windows 1252.
Now we need to open the newly edited file in HEX - you can use EditPad Pro for this, or another hex editor. You
should see two new bytes in the first 2 places in the header, right next to the word PAPA - FF FE. Delete these bytes. If you don't see them, try re-opening them or opening them in another editor. Sometimes it doesn't update immediately.
Now find yourself a diff tool. For simplicity's sake I will refer to
http://www.diffnow.com/. Upload the backup of the original file you should have from earlier, and the file you just finished editing. We will compare them to ensure nothing else in the PAPA file was "damaged."
If everything went well, you should see that nothing is missing, and the structure of the PAPA file has not been compromised. This diff should show you that the only thing that has changed is the text or word you edited or removed.
So that's how to edit a PAPA file. I think it would be easy to write a program that does this for you. All it would have to do is change the encoding to/from UTF-16 LE while deleting the extra 2 bits. It would be up to the user to leave the other extra characters alone.
Now, as far as ADDING new files to a .xbb, I don't know, but if I were you, here's what I would try:
Open a .xbb, like Msg.xbb, in EditPad Pro. Convert it to UTF-16 like you did above. Scroll all the way down to the LAST entry (or tag) for the last PAPA file. Copy any special formatting and characters with it, such that you have two copies of it now, including special formatting characters. Rename the entry, do whatever, save it, convert it back to Western 1252, delete FF FE, and check it against the original with diffnow.com. I don't really know if that would work for adding new files to the .xbb, but I suppose it's a brute-force way to try doing it manually. If it works - great! If not, well, I'm not sure how it can be done - this is only my best guess. It's more of a hypothesis, because I haven't been able to try it myself yet. But at least you should now be able to easily edit PAPA files, so that's nice.
Let me know if I need to clarify anything.
EDIT: Eh... Okay, so about that part where I suggested a way to add things to the .xbb... I crossed it out because the .xbb structure doesn't look like how I thought it would. You can still try, but I just got the chance to look at it myself and I can't guarantee that will work. I can't make much sense of it, actually. There's a lot of random Japaense/Chinese characters that are probably used for formatting, but I wouldn't know what to do with any of them. So sorry, I don't think adding more to it can be done
But editing the pp-files should be pretty solid. About to test it actually. I'll edit this post with my results.
EDIT2:
YEEEEEESSSS!!!!
As you can probably tell, based on my excitement, editing the PAPA files directly does work in-game. In fact, if you wanted to save yourself some time and effort, you can actually edit a .xbb file, using the same process as described above, without extracting/decompressing it! I only changed one line for testing purposes, but no other lines of data in the .xbb got damaged or missplaced. So my changes are visible ingame and nothing else is broken. I'm quite happy