Not sure you ever could
I don't believe casino security ever could backroom people just for advantage play. It's for suspicion of cheating, and only for the purpose of detaining you for police. So if they try to backroom you, and you sit in your chair and say "If you think I've done something illegal, call the police, I'll wait right here for them" there's no reason for them to touch you. It appears any backrooming of AP's they've done has been something they've gotten away with, which is slightly different than something that is allowed.