Your NHS number is not related to your visa - it is assigned to you when you register with a GP and is yours for life, so it can never change. It’s simply a way to identify you/your medical records in the NHS computer system.
British citizens born in the UK are assigned their NHS number at birth, while people who move to the UK from another country are issued their NHS number when they first register with a GP.
Sent from my iPhone using Tapatalk