To exclude them you'd need to prove you had a legitimate reason and it was proportional (proportional means of achieving a legitimate aim).
Protecting women & girl's safety, dignity & privacy whilst changing so naked/showering would seem legitimate. Providing available private changing rooms for people who identify as transgender regardless of medication and/or surgery alongside single sex space seems proportionate.
JackyH wrote of women's toilets so one presumes this is also the case for female communal changing rooms:
"If a person does not have a GRC they should be treated the same as everyone who is of that same natural sex. Thus, a male who transitions should be treated the same as any other male and vice versa. Anyone can ask to inspect a person's birth certificate to check the sex reference. If a male who transitions has a BC that reads as male he should be treated as a male.
There is no law about his use of toilets so there is zero requirement to allow him to use any of the women's facilities, even if he does have a GRC. It only takes one woman to "reasonably object" to have any man removed from any women's facility / service.
EqA, Schedule 3, section 27, subsection 6: (6)The condition is that—
(a) the service is provided for, or is likely to be used by, two or more persons at the same time, and
(b)the circumstances are such that a person of one sex might reasonably object to the presence of a person of the opposite sex."