I haven't tried because you haven't said how to do it yet.
I'm assumed you couldn't edit pants colours since you ignored my PM. So I investigated more into it and it looks like all the warmups share the same pants texture. The colour is locked somewhere and I have no idea how to change it. Probably somewhere in the games memory, which I probably can't change since the SYNC.bin fucked us over.
BTW, to change a iff file that a team uses you're going to need to get into the Team block.
You can do this by finding a team name address, and the right clicking it and press "Browse this Memory Region". Then you can find the f000.iff and change it to whatever you want.