You can change markers on any identity document (except birth certificate) without a GRC.
None of which changes affect your legal sex, which remains whatever is on your birth certificate.
A GRC changes the legal record of your birth.
And no, that will never stop being insane.
When I say that gender has replaced sex on all documents regardless of if they purport to have 'sex' on them, it really is true. Millions of us are assumed to have a gender, and it's on all our ID, in the place where our sex used to be, purely for the benefit of the people (of the opposite sex) who want to be documented as matching us.
The litmus test of whether a marker is sex or gender isn't what you are told it is.
It's much simpler.
Can that marker be changed from M to F or vice versa?
If yes, it's gender, not sex.
There are no markers left on official documentation that I can think of, that are not permitted to be changed to something opposite to ones biological sex.
Ergo, sex is no longer being recorded. Anywhere.
Gender is in its place.
People just haven't realised.