Yes, you can change the music, and you can use SubDrag's N64SoundTools to do it. The format is N64PtrTablesV2.
Although his tool can alter sound in-place, it has the limitation of not being able to exceed the original bank's sound. You can use a dummy file though (basically a blank file of absurd size with the right header, or an extracted one), edit that, then insert it into the filetable like any other data (teams, images, etc.). Filename has to be the same for the stuff to be found.
Actually, you can also insert the announcer callouts for teams the same way. Filename should be the team's name. Look at existing ones for a reference. It doesn't use hard IDs to them, only filename lookup. Only trouble is getting some nice, clean source to work from, otherwise I would have done it for the Texans.