“1) She is head of the Church of England by law and is required to be a member.”
Who represents the CoE, if they go into schism? The Queen hasn’t left the Church, if the Church chooses to rejoin Catholicism. She’s both Catholic and a member of the CoE.
“2) Under the Act of Settlement (1700) that governs the succession to the throne she and her heirs are barred from entering into communion with the Roman Catholic Church, on penalty of losing their succession rights.”
Again, this would apply if she were to convert. If the entire church converts, then really, the Act no longer makes sense anymore.
3) Under the Statute of Westminster (1931) the British Parliament cannot alter the succession to the throne without the permission of the other dominions. Therefore amending the Act of Settlement would require the agreement of all the other Commonwealth Dominions that recognize her as head of state.
This is the biggest problem. I do not see significant support for the Act of Supremacy in the colonies. Especially not here. She’d be Queen of Canada before anywhere else.
“Until the law is amended she is by law forced to be a member of the Church along with women priests and gay bishops. As are her children and grandchildren if they wish to assume the throne at some time in the future.”
What happens when the CoE itself splits? I don’t see any clues from the Act of Supremacy.
What can I say? See post #28 above.