A friend of mine had a family member wet sand his 911 coupe. It was black. It came out perfect and it was easy to reverse it. (compound and polish the car).
I wouldn't say that you can safely do this more then once because there is only so much clear on the car and you remove it when you wet sand it.
When he was done w his car, you couldnt tell the difference between a matt black lambo in my showroom or his wet sanded porsche regular black. They looked identical.