Thanks. It is interesting to see that Prince Knud's protest cited the treaties which formed the basis for the 1853 Act of Succession, just as his
appeal to Stalin on the issue apparently cited the international agreements at the Congress of Vienna.
It is true that there were treaties with Russia and other European nations concerning the Danish succession in the 19th century, but did those treaties remain legally binding in 1953? If so (I haven't seen the treaties) would they mandate male succession in perpetuity as Knud suggested, or would the conditions be satisfied provided the succession continued to follow the descendants of Christian IX? In practice, whatever the 19th-century treaties state, it is hard to imagine Stalin, Churchill, et al even thinking of intervening on Prince Knud's behalf. But it might be interesting to see what the conclusion would be if one of the male-line Rosenborgs were to sue to claim the Danish throne.
ETA: It is also interesting that he protested on behalf of his teenage sons; does that indicate they shared their father's views?
Theoretically, but I assume that the people who want Queen Margrethe II to be followed by an agnatic relative instead of her son would also want Sverre Magnus to inherit the Norwegian throne instead of his sister.