Transgender preacher

If it were me in the situation, I'd probably want to act as my identified gender (not birth gender).

Since we both have feminine and masculine energy it seems to me it would be most appropriate to act in accordance with the one they identify most with as I assume they would be more drawn to the energy of that gender despite their birth gender.

But, as others have said, it's going to depend on the coven. Or they could always start their own!

It matters a very great deal in certain covens and Traditions. It is by no means "just a label". It defines the person's relationship to the God or Goddess, the channeling of specific energies, and a representation of the Sacred Marriage which is central to Wiccan belief and practice.