There are mixed schools of thought when it comes to painting plastic body panels. Some will tell you that you need a flex additive in the paints... others will say it's not necessary.
If it were me in your situation I would have the color re-done and then have it cleared. Then you know that the different types of paints are, and you know they work together.
If you are planning to get the color redone.... as long as the prep is done and a good primer/adhesion promoter is used it shouldn't be a problem to use pretty much anything over the old paint. This assumes that the prep sanding gives a good surface to paint on. Any orange peel, bubbles and what not need to be gone.
But if you are hoping just to get a clear coating done.... I don't really know what to recomend I'm afraid.... especially since most shops will have there own preference to this that or the other thing anyway. So even if you come in saying I want you to use this type of paint.... they may not be willing to do it as it is an unknown to that particular painter.
All I can really suggest is to find a trustworthy shop and talk to the painter. Show him/her what it is you need done. It's much easier to figure it out when the painter is able to "see" the problem
