For your name, enter "SOUND." A music option will appear. Press Up or Down to change the sound, and press A, B, X, or Y to start the music.
Opponent Switch
On the "Select Player" screen, choose the "Name Change" option. Choose to alter the name of one of the players already listed, then press Down on Controller 2. Change the name as desired, and then press Down again to get to the other opponents. Press Start whenever you are ready to race.
Instant Cash
For your name, enter "SETAUSA." This will let you start your first race of "Grand Prix" Mode with $10,000 to spend on parts.