Descartes wrote:
You don't legally change your religious status, that is a personal matter. It's not like getting a sex change.

Not in north America, no. But some places..
But things such as baptisms do register you as member of a certain faith, and even certain diocese, in the example of Catholics. Regardless of whether or not you have attended church in 50 years, or if you drink the blood of small animals as part of your
new faith, your baptismal record is used as a counter to announce the strength of that church.
You have to fight to get them to give you up. You are worth money and influence to them.
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davidred wrote...
I installed Ubuntu once and it completely destroyed my paying relationship with Microsoft.