That is the choice of the individual (assuming they actually received the "memo"...).
And while I may not agree with Mormonism, this shouldn't be about religion. This is about counting citizens of a state (and illegals should NOT count in any way but how many busses and planes are needed (or train cars?) to sent them back to their country of origin.
I agree, must as LDS beliefs are anathema to my intellect, - wouldn’t the US embassies in these foreign countries know or their consular offices in the US?