I don't know if they've changed their minds, so much as force a distinction between sex and gender, where sex is female, and gender is woman. Therefore, they can support the idea that females have sex based rights, but in practice most situations, women (including TW) have gender based rights, too.
So staff toilets are a gender based right, and asking for a female hcp is a sex based right?
This is speculation of course, and the distinction seems to be entirely based on the transperson informing the guidance.