Dresden Files: Winter is coming (Cold Days Spoilers)

[Tavar]

Except that once a Changeling chooses, they literally and permanently transform. They become either 100% Fairy or 100% Human.

Right....but they are not born a Sidhe. If they were, they would not have to chose, because they would be 100% Fairy. Words actually mean things!

Molly is 100% Human. The question is does the mantle turn her into a Sidhe (The "Fair Folk" species of Faerie that most of the Winter and Summer court nobles seem to be, as opposed to Trolls, Ogres, Centaurs, ect), or does she remain primarily Human.

Perhaps looking to the books, where we have Mab, as well as possibly the former winter Lady to provide examples.