Can You Get Unchristened?

No, baptism is immutable. ... When you reach the conclusion your church worships a god that doesn't exist, then logically baptism didn't actually do anything to you. Becoming unbaptised would be as pointless as the original ceremony.

What does unbaptized mean?

: not baptized unbaptized infants also, dated : heathenish, profane … men cling to this old song, because they still have moments of unbaptized and uncommitted life, which give them an appetite for more. —

How do I excommunicate myself from the Catholic Church?

Process of Excommunication

If you want to be excommunicated, you have to go through official channels. Your local priest can't help you; instead, you must write a letter to your bishop. Tell him where and when you were baptized (they won't excommunicate non-Catholics).