How does a course get the royal title?
I think it is as simple as a member of a royal family playing or visiting, in an official capacity. They would move to bestow the royal tag at that time or at some stage shortly after.
There is a great story about how Royal Queensland won the tag, decades ago.
Royal Melbourne, Sydney, and Adelaide (all state capitals) had already been anointed. Brisbane (Queensland's state capital was rumoured to be next). Officials from Queensland GC allegedly intercepted the royal party on arrival into town, and took them to their course, instead of Brisbane GC, and subsequently, earned the royal mantle.
Wonder if it's true?
It happened decades ago and is possible....
Matthew