Okay, good news! I've successfully been able to unpack, edit, and repack the text files!
Tool here:
https://github.com/vgmoose/GARC-Unpack/releases/
And here's a 2006-esque ROM hack demonstrating it:
To fix the ROM packing, I had to subtract 4 from the offset outside of the modulus. (see source) I know it works on text, not sure about other files.
THANKS A LOT!
turn into ash or something lol XD