Over her lifetime, the Queen has been commonly known as "Princess Elizabeth of York", then "The Duchess of Edinburgh", before becoming Queen. In my proposal her OC name would change to "Queen Elizabeth II" with "former names" listed as above.

Those are titles, not names.

Isn't that inherent with monarchy, though? I still think we should change (at least the major royals) to reflect this.

You'd probably want to make a Duke/Dutchess of Edinburgh Container and then Races for them.