I remember one time someone called me transphobic for writing a Rule 63 fic in which an originally male character was turned cis female.
And here’s the deal. If you wanna write Rule 63 where the person is cis female, it’s fine. If you wanna write Rule 63 where the person is trans female, it’s fine.
Because they’re generally different, unless in your fic world, the transwoman was raised a woman from childhood, and did not transition later in life, getting the upbringing of a cis woman in the same society.
I wrote a couple of cisfem Rule 63 because I was fascinated with how different the character would turn out in terms of upbringing without changing their more important characteristics. Would this cisfem character have a father who didn’t hate them because they were more kindly inclined to a daughter than a son? What are the societal restraints placed on this cis woman? How would certain characters treat this cis woman, if they treated the original cis man a different way?
I don’t really write too much porn, and even if I did, cis hetero porn does very little for me. When I write cisfem Rule 63, I do it on the basis of taking an established society and trying to worldbuild around what would happen if Male Protagonist was born Cis Female.
Quite frankly, I’ve also done trans female Rule 63, with the same character, with the same purpose. I want to think about their upbringing, and at what point in their lives they transitioned, and how different people and their society as a whole would react to transness. The concerns and the cultural impacts were unique.
It’s a fact that most (even if not all) cis and trans women are raised differently based on their culture and society. Transwomen will often be socialised and brought up as men in their family and society, even if they aren’t, and their transness will add its own individual cultural story thread, as well as their life after transition. Ciswomen will, in general, not be socialised as men, so the upbringing of a cis and trans woman will be different depending on the world they live in and their youth and subsequent growth.
Long story short: Writing CisFem Rule63 is not inherently transphobic. The only transphobic aspect is believing Rule 63 does not extend to trans people; which it does.
Genderbending should be trans (and enby, under the trans umbrella) inclusive, just as a general rule, but cis genderbends and trans genderbends can carry entirely different narrative elements depending on the writer.