If you end up having enough space, you could have the game choose a version at random, or you could let the player select between the two on the title screen or maybe they could switch between the two versions by using the right difficulty switch while playing. So the left difficulty switch would be for muting the music and the right difficulty switch would be for switching between the two versions of music.
If you have a ton of space, you could have more than two versions of music and let players choose which one they like by using the select switch while playing:
For that type of thing, you'd want to leave out the feature that lets players hold down the reset switch and the select switch to rapidly change the selection (since they could mistakenly reset the game if they're not careful). While playing, the reset switch should only be used for restarting the game.