The following commands can be entered in the "SELECT MUSIC" screen.
Code - Effect
P, P, while holding G - Changes difficulty from BASIC to EXTREME
P, G, G, P - Changes guitar mode from default to Bass and Open Pick...
G, G, G - Changes the note scroll speed from 1.0 up to 10 (MAX)
Hold start after selecting a music - Enters PLAY STYLE MENU
P, P, P, P... - Resets all play style changes to default
Push select button while holding G - Sorts the music list