Apparently a hundred thousand or so Britons have done it.
Or think they have done it. Would it be mean to point out to these newly certified heathens that baptism, by its sacramental nature, is irrevocable?
Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation. Given once for all, Baptism cannot be repeated.
(By the way, my wife and I have had five children baptized in the Catholic Church. It didn't cost us a cent, and we got not only an official certificate each time, but a nice candle as well.)