The interest I have in the apparent concern these people have with the Mormons, is not that it's mumbo-jumbo, but that it's internally inconsistent. It's a bit like being a Christian (or, at least, the sort of Christian who doesn't believe in the reanimation of dead people's physical bodies at the end times) and still reverentially burying or cremating dead bodies: your actions give the lie to what you say you believe.

First off, as long as it was widely known that the organisation in question made a habit of unilaterally and indiscriminately declaring people to be Japanese, nobody (no living person) would ever take an entry in such a book as good evidence of Japanese citizenship, or of lack of British citizenship. Secondly, even if the Japanese government declared this hypothetical grandfather (both mine were in the war, but in Europe/Africa) as a citizen, what's important to his/our sense of patriotism is whether or not the British government still think he's a British citizen -- and that would especially be true if "patriotism" included the belief that Japan doesn't exist. Or, de-allegorised, what's important to a Jewish person's sense of Jewishness should be whether the Jewish God thinks they're Jewish. A posthumous Mormon baptism can only de-Jew somebody if that's what Jewish law says happens, if Judaism gives that baptism authority, and given the history I'd expect Jewish law to be pretty solid on the point that forced, involuntary conversions don't actually count.

Peter