They do already. It's called the off switch. During the coldest days a couple years ago, they feared too much power was going to be used so they randomly were switching off power for 20 minutes throughout the area. Problem was, they'd either forget to turn it back on or when they did the surge blew transmitters. I don't think they'll be doing that again anytime soon.
Same thing happened here in TX last summer...they had just installed all the smart meters and they decided to try the rolling black out thing where they shut off your power for a few minutes in the middle of the night if they start to get near capacity...it blew a bunch of transformers as well...