Alright, sorry for the triple post but I've done it. Here's the link to all the tools you'll need:
http://pastebin.com/Au7Bh3tFSo, to make things super clear because it's a little complicated, here's how you insert arbitrary text of any size in to FMWI:
1. Take the data file you want to edit out of FMWI's data folder. Probably leave a backup.
2. Decypher it with my first program. Run it with the command line arguments 'data5.dat d'.
3. Take the output of that, and unpack it with my program. Run it with the command line argument 'decyphered.dat'.
4. Go in to wherever you put your copy of UltraCrypt and run the example game in game maker. Choose one of the unpacked files, choose to decrypt it with the string bV.
5. Finally, you have a single file that you can edit. Put in whatever text you feel like.
6. Reverse the decryption by doing step 4 again on your now edited file.
7. Reverse the unpacking by running my packing program with the command line argument 'decyphered.dat.gsty'.*
8. Reverse the decyphering by running my cypher program with the command line arguments 'repacked.dat c'.
9. Oh my goodness, you're done.
*Whoops, couldn't be bothered changing the file extension to .gste, doesn't matter thoughAnd a few closing thoughts:
I've done only the smallest amount of testing on my programs (editing Yukari's first line to say "I am terse.", which worked fine) so maybe they still aren't perfect.
I have absolutely no idea if they work on any data files other than data5! eh it seems fine for other data files too, phew
Actually, on that note, I didn't even include usage information for unpacking and repacking data2-1 through data2-3, and data6-1 through data6-3. I haven't tested that, but it should theoretically work the same way it did for Yamsman's code.
I'd like to reiterate that I would prefer not to lead the FMWI patching project (as it were) from here on, because I want to avoid spoiling myself by reading the translation LP. Someone recently PMed me asking how they could help with the patching. Well, I'm happy that you're enthusiastic, and I think you could help everybody copy and paste the translation from the LP in to the game files. But I don't want to be the person that you report to!
ugghh of course it was unpack then decrypt, not decrypt then unpack