To apostatize.
noun.
One who is guilty of apostasy; one who has forsaken the church, sect, party, profession, or opinion to which he before adhered (used in reproach); a renegade; a pervert.
noun.
In the Roman Catholic Church, one who, without obtaining a formal dispensation, forsakes a religious order of which he has made profession. Synonyms
Unfaithful to religious creed, or to moral or political principle; traitorous to allegiance; false; renegade: as, “the apostate lords,” Macaulay, Hist. Eng., i.