My concern with changing the sex at birth field to female, appart from the DNA issue, is that it would not be accurate, and if I were to forget to change it back, it might confound current or future genealogists. Nor am I crazy about setting it to blank, or setting the "other/do not display" status, as that tends to suggest that I am agender or nonbinary.
I had earlier considered the option of putting my current legal name in the preferred name field, but that does not feel satisfactory at all, since it is now my legal name. I ended up entering my legal name in the name fields, and writing a note in the biography section where I mention my name given at birth. Again, this seems problematic for genealogists and for people searching for me in general.