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.

I should probably explain the "luck" value.

The game uses a lot of "die rolling" to determine pass completion, interference, tackling, etc.  The luck value only applies to receivers, and it's a modifier for the success of these rolls.  If you try to tackle a receiver this value is read, if they shoulder a guy this value is read, etc.  Oddly, it's the receiver's luck that's checked when the ball is passed to them, not the guy who threw it.  So, as strange as it may seem, somebody trying to intercept the ball during a pass will be less successful if the guy you're passing it to is "lucky", despite how crummy the passer was.

I did have one question: is a player's first name ever used in-game?  I haven't found a reference to it yet, and if it isn't used clearing those names out would double the number of possible additional teams from 15 to 32--almost doubling the number of teams.  Granted it could be increased more with effort, but it's sort of a ludicris number to begin with.

The amount of data stored that isn't used is rather amusing really.  Position numbers aren't used, there's a placeholder for a filelist ID for a face that hasn't been used since the original, one of the 3-letter names isn't used, as are the values for the linemen or defense outside of displaying them.  Except for the special team value and difficulty factor, no team stats are used during gameplay; they're exclusively for generating simulate data. 

In that regard, it turns out the game is remarkably fair despite the wildly different team values.