Does anyone know if the bumper can be sanded and then painted, or does it have to be painted over the original paint because it is plastic?

The story is, I got a 1cm by 3cm chip in the paint, I dont know how but I did(cheap paint). Well anyway I took it to the dealer and he had it painted but the guy did it at Acura and did a bad job so I took it back and they took it to a body shop and they polished it and clear coated it and now you can see a line where the paint changes so now I have to take it back for a third time for them to repaint and clearcoat the whole thing, but I want to sand it if possible. Acura has been really nice about it and got me a rental car each time. By the way yacht + 4wheels=LeSabre. The body roll was horrible but the ride was compliant. I was so happy to have my TLS back and now I have to give it up again.