Could a Baptism be Null and Void based on Circumstances?
In the current round of CO visits with the BOEs, there is a specific point regarding this that is read to the elders. I don't recall the exact wording, but the gist is, "if anyone tries to come up and say they want their baptism nullified, they're SOL. We don't 'do' baptism nullifications".
And there were also some references to some Watchtower articles from the 50's or 60's. I did not look them up.
There was another poster (don't recall who) here who explained this in a little more detail, a few months back.
I.e., the GB are well aware of this particular kind of "trick", and are forewarning the elders to watch out for it, and are telling them not to allow it.