Dear Rabbi, is it permissible for a Jewish actor to play in an idolatrous role? Maybe it can serve a constructive purpose by presenting the nonsense of the idolatry (even in a movie directed by a Jew). Thank you very much!

You can play the role, for everyone knows that you are just acting. Nevertheless, objectively, under all circumstances Jews can't wear a cross nor enter a real church (if it's just a stage, it's ok).