With the rather fast sad end to the "Black Knights" event (which I got to experience a whole 10 minutes of before it was pulled due to too many complaining) I thought of an idea:-
An Event theme enable \ disable toggle button!
Enabled - Event themes are active on your islands.
Disabled - Event theme are turned off on your islands.
When event themes are turned off even the island wide event buffs can't be applied. Players can still take part in the event as normal. E.g. during the Christmas event the island wouldn't be covered in snow, but the Christmas collectibles etc... still appear as normal.