hmmm, I'm not sure PC-ing over paint is the way to go: typical PC is applied to bare metal right after blasting so there's no contamination that could prevent the PC from adhering, then it's baked at around 400º to melt and fuse. If you have any paint underneath it might burn off or just run into the PC, I am not sure that anything from a paint pen can take that much heat (I'd be looking for a high-heat engine or BBQ paint if I was trying, but I wouldn't try it). Why not apply the lug-lining paint on top of the PC?