Good answer on the MEK. I have used lacquer thinner to cut the glaze on PVC pipe before painting. It doesn't leave scratches, but you do want to use a fairly lint-free rag to do the wiping or you will wipe fuzzies into the surface. Its also nice to get the printing off the pipe in advance of painting so that it covers evenly. You would be surprised how much dark letters on white pipe want to show through some colors.
I wonder if that Krylon paint for plastic would hold up better on something other than lawn furniture. I imagine lawn furniture wants to flex. I have some shutters I wanted to try it on, but now you have me paranoid. Other than the work, of pulling them down and cleaning them and painting, I guess I am not out anything. If they start to peel, they will have to be replaced....which is the only other alternative for changing colors anyway.