I'm interested in overridding MiningQuarry.EngineSwitch to disallow people from turning off a quarry if they aren't authorized. Is it possible to just override that method or would a hook like CanSwitchResourceExtractor need to be added to the game and then a plugin could be created to override that hook? 

You need to use hooks. Or force somehow the code to use your class instead of their one :)

No hook currently exists, it seems like the developers would have to add something to use the hook.

I once tried to do this to lock the quarries on.  DIdn't find a good way to do it.  Settled for setting a five minute timer that turned them all on.