I was thinking: how about making it possible to send missionaries to other nations at a higher cost and/or lower success chance? Doing so could give the nation a temp cb against you and lower relations (if the nations is a religion other than your own).
Alternatively, this could be possible for defenders of the faith only - as that option currently ain't worth much.
Alternatively, this could be possible for defenders of the faith only - as that option currently ain't worth much.