It's blunt insanity.
Girls, the boys will be changing in separate rooms because privacy, dignity, this is important for all of you, we believe in this wholly and have policies about it, and will never permit for any of you to be uncomfortable or at risk by mixing the groups after a certain age point.
Oh, this boy now prefers to identify as a girl?
Girls stop being so unkind and wanting privacy and dignity and safety! Your objective experience of changing with a boy must be completely dictated by this boy's subjective sense of self, and your priority is not you but him. Your boundaries must always be predicated on whether or not a male person agrees with them, and if they are sad and upset by your having needs or feelings that you'd like the male person to respect in return then you are being a Very Bad Person.
It's male supremacism, there is no other term. It is that plain.
No. The male child should absolutely be provided with somewhere separate from the other male children if preferred as no one should have to change without feeling dignity, privacy, safety, and that applies to equally to females not just to males.
The female children's feelings and equality is not some kind of ritual sacrifice that adults must make to a trans child to demonstrate sufficient care for them. No child in this situation matters more or less than another one does.