As far as I know, there are two parts to the question: firstly, asking about gender at birth and, secondly, asking about any change.
That would be fine but it isn't what's happening.
The first question will be asking about sex, and the guidance will advise that self-identified sex is acceptable.
This is not about a simplified legal process, is about people simply saying they are the opposite sex and having it legally accepted.
You can be sure that its use in the census will be quoted as a precedent in other situations.
Memories of the Swinging Sixties
Good Morning Saturday 3rd June 2023