Most the time cove is painted with a trim paint- a satin or semi gloss.
If it is presently painted with a hard shiny paint- sand it lightly to dull the shine for adhesion.
If you know the paint is an oil enamel, and you are going to a waterborne finish, I recommend also priming it with a good adhesion primer after sanding. A good grip is really essential- and the first thing to hit it is what will give that.
"It's better to come here with questions before you screw up than to come here after and ask how to fix them."- JS