Protocol - the official procedure or system of rules governing affairs of state or diplomatic occasions.
At offical functions when Mr Corbyn becomes Prime Minister he will be representing the country - not himself.
For example, whilst in the past he has always worn a white poppy on rememberance day, protocol dictates he must now wear a British Legion red poppy. Once he retires as Prime Minister or as Leader of the Opposition I think you will find he will once again wear a white poppy, unless, that is, performing offical state functions as a former Prime Minister.
The country has to come before the individual when holding such high office. Like I say simple.