..I was thinking about this some more. Micro is correct, that when OOTP updates it will replace your sound folder. So, if you wanted to spend the time, you could create custom sound folders for as many parks as you like and swap them in / out for each series, depending on which park you're in or which team you're playing
e.g.I could create a "Beat L.A." chant to play at ATT Park when the Dodgers are in town.
Now if we could get the devs to add a tag for Home run events, I could then have a foghorn sound triggered (mind you, the Giants don't hit that many HRs these days)!!