Hi, it's me again. After some experimentation with a modified version of the Lua decompiler (and incremental recompiler) 'LuaTool' (originally meant for some Windows Mobile application), which I'll release including source code at a later time, I've managed to make a small 'useful' modification.
With this modification (modifies
SchoolHallways.lur) the School Store has all clothing items that are purchasable in the other stores plus its own stores, and each for only $0.01 -- and as the game doesn't count money that precisely, it comes down to a reasonable $0.00.
Installation of the script should be done using G-IMG, ImgTool or any other application capable of replacing files in GTA: VC IMG archives, and it should replace SchoolHallways.lur in Scripts\Scripts.img. Don't forget to back up the original Scripts.img and Scripts.dir files -- you don't want to have to reinstall Bully.
Tools and a small tutorial to do exactly this will be released once I iron this stuff out a bit more. In the meantime, enjoy!