Why would the speaker say "if he chooses?" Is it common for monarchs to change their names?

Native speaker’s answer
Rebecca
Yes, it is common! When someone in line to the British throne takes over the throne, they have the chance to change their name to whatever they want. For example, King George VI was Albert Frederick Arthur George. So if he wanted to, or "if he chooses," he could change his name. Queen Elizabeth the 2nd chose to keep her own name, as did her son, Princes Charles, now known as King Charles the 3rd.