Like Barbara I am not sure that the clasp of the Hanoverian pearls and the one worn by QEQM at the christening of Prince Michael are the same.
We have very few photos showing the clasp of the Hanoverian pearls worn at the side or the front, which gives a different perspective from the clasp sitting flat at the back of the neck.
In photos of QEII wearing the necklace the two strands of pearls appear to be equidistant on the clasp.
In the 1942 photo of QEQM the two strands appear to join the clasp in a closer formation - that is with less space between the two strands. Like Barbara I feel that the clasp is larger on this necklace. I also have the impression that the central gem is larger, while the border is narrower than in the Hanoverian pearl clasp.
If QEQM was wearing the Hanoverian pearls then this is a most unusual style for her, although HM did wear her pearls with different clasps showing at the side throughout 1935.