Reformation is hard-coded as a Pagan mechanic. It might be possible to make a reformed version and an unreformed version, then rebuild the whole reformation mechanic manually. You'd probably have to have the reformed version be its own branch of Christianity to stop it from appearing as a heresy, then change parent religions around when you reform. Don't know how to make them lose the +20 Moral Authority for being a reformed religion, short of a maintenance event that applies a -20 MA penalty repeatedly.