referring to that you said about changing the main.scm and that all savegames won't work anymore
Well I did, I didn't know of this, but I figured out myself that if I change a vehicle in one mission it will be much easier to do (I know sounds like a cheat, but I was really stuck). Enough of this, I wanted to say that all the savegames was function properly, I didn't noticed any glitches or bugs.
EDIT: Now I noticed that if I ADD some lines to script then it really becames unuseable by previous savegames(I can play but I wont see any difference ) but If I start a new game, then it(the my modification) will be working.
So isn't there any way to add new stuff, but still be able to use with previous savegames???