Is it possible to mod sound effects?

I was thinking of making some new sound effects, everything from basketball dribble sounds, horns played over the loudspeakers, etc.

Is there a tool that allows access to the game's audio files?

As far as I know there isn't one at present. You might want to check out this thread for some ongoing efforts to find a way to modify the game's sound files:
viewtopic.php?f=149&t=91435

what sounds would you change besides in game music and possibly team names?

what sounds would you change besides in game music and possibly team names?

Basketball dribbles, dunking sound effects, crowd noise, crowd chants, pretty much anything I can get my hands on.