Thermostat change

Definitely. Engine parts won't expand to fit properly so excessive wear will result. The coolant will take longer to get to normal temperature. When it does, the computer controls go to "closed loop" where it fine tunes fuel metering based on readings from the oxygen sensors. When it stays in open loop, emissions will be higher and fuel mileage will go down.

The higher temperatures also reduce blowby and that which does occur is more likely to vaporize and be pulled out and burned rather than cause sludge in the oil.

If there is a problem now with engine temperature, you need to diagnose and repair that problem. Changing the thermostat to a lower temperature isn't going to fix an underlying problem.