After undergoing sex change surgery, the person is no longer the same. They are no longer the man or woman they were, they are now a new person with a new gender. That means the person has to change everything and get ID and other things like that. In a way, the person is born again. They would have to start over and get a whole new name, a new driver's license, a bank account, medical records, birth certificate, social security, credit cards and other things they need ("medical") ). People who have chosen to achieve the very long-term goal of having surgery are probably aware of the time and patience they must devote for everything to change. All legal steps to do this also vary from country to country.