Thermostat control in a rental here in MN

[Aaron Harren]

Does anyone on here know if it is legal for me to put a lock on the thermastat in my duplex?  The stat is on the main floor and controls both levels.  The new tenants love to have the heat cranked way to hot.  Can I put a lock on it so I can set it to one temp? Or maybe put a wireless stat in the house so I can adjust as needed remotely?

Thanks Aaron