Can I paint over gloss paint with emulsion?

Question:The previous owners have used gloss paint on the coving in our bedroom. We can't decide whether to just replace the coving as its not in great condition, but we have lath and plaster ceiling so may be a bad idea. Not sure if the coving is plaster or polystyrene so not sure whether we can strip the paint off. I wondered if I sanded it down well, whether matt emulsion would go on okay. Any ideas much appreciated. :)

Answers:
if the sanding doesn't work... try using Kilz or Bin or Zinseer.. as a base primer then paint over it. That should work