Apologies for 'necroing' this thread, but I think I have an important point to add.
I have a family member who was born physically male, married, had three daughters, divorced, legally changed sex to female, has a female birth certificate now.
The solution of showing them as female from birth will cause serious implications with their ex-wife and at least one of the their daughters. The ex-wife is also an Ancestry user who not like appearing in my tree as having been in a lesbian marriage, and one daughter in particular would have serious issue to appearing to have had a sperm donor father as a result. Neither also want me to hide them in my tree.
Ancestry needs to support 'Change of Sex' in some way.