Isn’t there something called self-excommunication?
Is what you are talking about the church process where a person has to fill out papers for an abandoning of the Catholic Church and then have a hearing in front of a panel of priests to see if it is accepted and then granted?
But what about the mark of the Catholic Baptism. It is always present on the person’s soul and will be a blessing or a curse at the time of their particular judgment and then the final judgment?