WordNet sense 1 (the state of having rejected your religious beliefs or your political party or a cause (often in favor of opposing beliefs or causes)):

apostasy, defection

WordNet sense 2 (an act (spoken or written) declaring that something is surrendered or disowned):

renouncement

WordNet sense 3 (rejecting or disowning or disclaiming as invalid):

repudiation

WordNet sense 4 (the act of renouncing; sacrificing or giving up or surrendering (a possession or right or title or privilege etc.)):

forgoing, forswearing