I know some folks have gotten away with this, I would avoid it. I generally don't put Krylong over either Testors or Rustoleum, but can put Rustoleum or Testors over Krylon. The new Krylon might be more forgiving...

In my case, it was just ugly--the Krylon crinkled up and blistered. Even after multiple efforts to sand it off and apply a covering coat of primer, I still had trouble.