Okay, so again, you've yet to explain why we must have people use the bathroom based on what genitals they have. There is literally no reason to do that. Transgender people like myself have been using restrooms with the rest of you pretty much since the inception of public restrooms. So I'm not sure why we all of a sudden need to force people to use a certain restroom. It's a solution to a problem that doesn't exist.
Like I said, I go to the restroom, go in the stall, pee, flush, wash my hands, and I'm out. Nobody sees any genitals, no confrontations.
Forcing me to use the men's room because I have a penis only puts me in danger, and literally for no benefit whatever.
Likewise, you don't even have the terminology right a "pre-op trans-man" (your wording) has a vagina, not a penis. Therefore under your rules would have to use the restroom with women, even if he looks like a lumberjack. A pre-op transwoman like myself would have to use the restroom with the guys, even though I'm in a low cut dress and heels... I don't see how that logic works. Why not leave it the way it is? Why make a solution to a problem that doesn't exist?