I was told - by the local guy that reconditions returned cars - that ANY modifications (tint, PPF, hitch, etc) WILL be removed - he had no flexibility on that. He also said the owner returning the car is "supposed to" be charged for the removal; but that wasn't as firm - I got the impression that they may or may not charge, depending.
No actual experience though; I just returned a lease, but didn't modify the car (largely for this reason).