Thanks for the answers. I have a few more questions thought:
-I wish to create a Rival that changes gender depending on which gender we chose at the beginning, much like R/S/E. Is it easily doable in FireRed, or would I better off doing it on R/S/E?
-I'd like to have multiple kind of battle musics. However, I'm not sure how it works, and if it's possible to have more battle musics than on the original (like 3 Trainer themes while still keeping the other themes). Is it possible to do that?
-Can I apply an IPS patch (from, let's say, a hack that has all the moves from 4rd/5th gen and physical/special split) to a rom, make a Hack out of it, and create an IPS patch that will work on the original?
Thanks in advance for the answers again.