Song/instrument selection for customizer

[SonicSBL]

The track theme customizer is nice, but I don't like having a randomly selected song on the currently selected instrument. Not every track element appears on every instrument or song. With that said, I'd like to be able to select my instrument and song before entering the customizer. This would save some time and effort tracking down specific elements that aren't seen often, like Big Rock Endings and Pro Guitar gem colors.