I think there might be some kinds of paints that would work. If the coating is some kind of polymer you might be able to find something that bonds to it. If it's Teflon or some kind of resin then you're kind of screwed. No real way of getting around that, unless you mixed the paint with it, and that would be difficult if not impossible. Besides, you wouldn't know what kind of coating it was by looking at it... Most people blow it off because it's expensive, and not very cost effective unless they're already spending a lot of money to cover or remove the artwork. Resin based coatings also yellow over time making whatever they're covering look old and nasty.