It's never been available for me, no matter when in the story I try.
No I mean at the character creation menu, you have to have chosen 'male' new+ doesn't count.
Haven't tested but my saves with the spells cock growth, and breast growth, despite being male and they never were anything else for testing purposes they cannot do the experiment.
Have tested, any modification done to a character via cock/pussy growth will remove the MTF event.
