It is not illegal, but it could lead to jail time.
Modern electric meters report in all the time. I can tell when the gardner hits the mower with his mower and knocks it off my house. I can see if someone hooks up a generator that doesn’t have a bypass. If you take a meter and put it on another home, the meter will stop working. Call for help and you’ll be taken to jail.
It’s not just stupid to play with an electric meter, but it’s also a crime in itself, even though no power was ever stolen.