Hi Moondoggy1111,
Thank you for posting in the community. I understand that you would like to install a new back plate and check if your Nest Thermostat will keep the setting or restart it all again. Help's here.
To properly set up your Nest Thermostat and the new back plate, you would need to do a proper factory reset and connect all the wires to the new back plate. As a suggestion, please take a picture of the previous settings before doing a factory reset to save all the features previously set up.
Here is a good article on how to factory reset your Nest Thermostat. And after that, please follow this article to set up your Nest Thermostat.
Let me know how it goes and keep me posted.
Regards,
Byron
