How does the Electrical Grid React to Large Changes in Supply or Demand?
What equipment would be involved in "rerouting" power to minimize the
  possibility of blackouts?


Transmission switching stations re-organize things when there are problems with generators or section of grid: -



As you can see, every generator connects to the (national) grid via a TS. This wiki page should help. Pictures taken from here
or here if not a Quora member