Don't get caught. It sounds like they will make your life miserable if they catch you doing that. It cost me about a grand to have a generator wired to the outside and with a specific box in the basement for determining which circuits you will run.
Yes, I updated my wiring and breaker panel a few years ago and added a transfer switch and the generator plug in box outside the house. I have a 6500 watt gen and have a 98% efficient 120v propane furnace that is wired into it along with the kitchen lights and outlets for the fridge and bathroom lights / outlets and deep freezer outlets and power vent outlet for the propane water heater. The basics to keep things warm and lit up and powered up where needed. The 6500 watt gen handles it well.
Before that I had a 5K watt gen and had extension cords strung all over hell and alternated things every few hours to keep fridge and freezers going, worst was doing that for over a week straight when we had the bad ice storm that knocked out power and tore down thousands of power poles and main lines all across the west side of the state about 7-8 years ago.
I have always wondered if you could wire your furnace so it is plugged into an outlet, then when the power is out you could just plug the furnace into the generator.
If one wants to listen to a generator beller and beg for mercy its fun to listen to them work like hell when you plug in something with a heating element like a coffee pot or toaster.::