Bonus track:
Press A, B, C, A, B, C at the custom cup options screen.

Edit driver:
Press A, C, A, C, A, C at the character screen. Select a character, then hold A and use the D-pad to edit their stats.

All cups and bonus track:
Enter HJACUY as a password.

Silver cup:
Enter JXPSVW as a password.

Gold cup:
Enter BEFQMR as a password.