Birth certificates can already be re-assigned. I have seen one - some years ago. However, the wrong facts are being recorded. If in reality a boy was born, called Mark, it is falsifying the official records to say that a girl called Marietta was born. If Mark married, say Jane, the marriage certificate should also be changed, to show that Marietta married Jane. Any children of that marriage should have their birth certificates changed too, to say that their father was called Marietta. Or maybe to state that each child had two mothers and no father at all. People who change sex may want to seem to have been the "new" person all their lives, but the falsifications can lead to an awful mess. Official records should remain exactly the same as they were originally created . Or else they cease to be official records at all.