Hello Duster,
Welcome to the Google Nest Community Forum. I'd be happy to answer your question!
Certainly, it is possible to replace a faulty thermostat with a new one without the need for a reset or restart. However, if the issue affects the functionality as a whole with controlling the HVAC system or managing the created programs, a reset would help to fix issues and recalibrate it.
Let me know if you have more questions.
Regards,
Mark
