Yes, every time I've opted out with TSA (which I do most of the times I'm required to go through the full-body scanners in the US rather than the TSA Pre metal

Yes, every time I've opted out with TSA (which I do most of the times I'm required to go through the full-body scanners in the US rather than the TSA Pre metal detector) I've been allowed to do so. It's often meant a long wait for an agent to become available, but I've never been refused. I admit to being a white male US citizen who politely requests it using the words "I'd like to opt out" (rather than some vaguer objection) and then waits patiently, not someone who gets angry at the officers. The ground rules aren't the fault of the workers, only any individual bad behavior.