I honestly feel like he doesn’t necessarily mean not transforming back. At the beginning of the chapter he almost punches the guy because he found out. I feel like part of the never reverting to his former self is partly not using violence to find answers to his problems and not being as careless as he previously was. I’m pretty sure he knows not transforming back is pretty much impossible and I don’t think he would want to stay as a girl permanently either. Also the chapter is titled end of the perfume, I feel like if he was never going to transform back the chapter title would be different if that makes sense.
It is true that some of these changes are less literally oriented around changing back and forth than of changes to perspective and behavior, I don't know what's going to happen, but I am not suggesting that this will be the last time in the story that they will change from one form to another, the fact that dressing more femme and not using violence are pretty explicitly socially "feminine" choices, it means they are committing harder to the role, they even say as much when regarding the clothing that it was a way to give them an excuse to chicken out and change wily-nily.
I was referring to what these decisions mean
thematically. The degree of dedication to a role and how that can involve a degree in changing perspective, perhaps even changing self-image, there is
potential for it to end up a permanent commitment depending on what kind of story the author wants to tell, what messages and ideas they want to convey, we'll just have to see where it ends up.
As to "not changing back being impossible" why? They have the support of the company building a new identity for them, fame has a way of forcing you to be conscious and "in-character" all the time, we've seen no indication of any magical or biological limits to the bath bomb method, you simply stay as your past life self until you use the undo version, the ties they have to their old life are... loose, a couple of women who maybe have a connection to that version of them, but also have connections to the new life, they seem to be pretty alienated from family and friends, the fact that they can even afford to functionally disappear for weeks at a time suggests that people aren't asking where the hell that guy is and starting a missing person's case, in practical terms, what does make remaining permanently in this other form "impossible?" genuine question.