How do I edit several different version of MAIN.scm together?

[VercettiGhost]

I have tried just doing the graphic changes in GPI (that is, installing everything about it except the main.scm) into the game, but then I lose the clothes, sabre, and weapon pickups there. But if I use the GPI version of MAIN.scm, I lose all of New Vice City's extra features. Is there a way I can isolate the certain parts of code to merge the GPI weapon and clothes pickups with the New Vice City scm?