Sounds like a risky place to be in, could blame it on a typing mistake haha, but people aren't stupid and I doubt anyone would believe it. Honestly, they'll come a point when they will want to see his certificates for music, it being a music course and all. Best thing to do is declare himself now to each uni and see what happens, he might be lucky and still be given a place for September at one or more of his choices. Depends on how each uni will look upon him lying in his personal statement but I wouldn't risk not declaring it, going to uni, them asking for proof and him not being able to produce it.