The real royal family name, Windsor, was changed to the fictional name Windham for the movie. Un-synched lip movements in a few parts (most notably the abdication scene) seem to suggest the change was made after the film was shot.
The Treason Act of 1702 by which Ralph has Lord Percival Graves arrested is an actual Act of Parliment, enacted in the last year of William the Third's reign. It made it a capital offense to attempt to prevent the successor to the crown from properly taking the throne. Eventually, in 1998, the punishment was changed from death to life imprisonment.
