Use Nest Protect to turn down temp on Honewell thermostat

I’m sorry, I’m not understanding what your question is.

Your Honeywell Thermostats have been to ST as devices that you control from ST

Your Nest Protects have been added to ST via installing NST Manager. These are your only Nest devices?

What exactly are you trying to do between the two? The Nest Protect simply monitors for Smoke / CO alarms.

Are you trying to control your Honeywell Thermostat temperatures from the Protect device?

Or are you trying to consolidate your Protects and Thermostats into a single SmartApp so you have a single point of reference for all the devices?

For further discussion around this, please post additional questions in the official NST Manager thread to answer questions specific to your Nest devices.