The Coronation Oath was revised

My what a question! The implications are staggering! Have you contacted the Home Office yet?

He was King George VI of the United Kingdom (of Great Britain and Northern Ireland)

Previous monarchs were styled "King (or Queen) of Great Britain and Ireland and Ruler of the British Dominions beyond the Seas" but by the time of George VI's coronation most of Eire had become self-governing and so had the Dominions of Australia, Canada, New Zealand and South Africa. The Coronation Oath had to be changed to reflect this. Also the part of the oath promising to defend the Protestant faith was revised to reflect the new realities (The Prime Ministers of Australia, Canada and Eire had demanded this).