Mine is screwed on. I think that's the standard go to, unless you ask for it I be stuck on. In which case I think they should do it for you. If I'd have known I'd have asked them not to put holes in her!
Mines screwed on, quite handy for taking off easily to wash behind, the 1st time I didn't take them off I was just jet washing away and the see through plastic peeled off, I stuck it back on but its full of air bubbles and looks a mess! I don't know why it peeled off none of my other cars have ever peeled and I didn't do out different! Haha as a funny note I did peel my mates rear bumper of all its paint with my jet wash! Haha