@signal15 Sorry for your significant meat loss.
You might want to take a look at the TempLeakSensor device luup files on the Vera for ideas. They declare a security device that can be armed/disarmed and associated temp and water events used to detect a freeze or leak respectively. In your case, you would create a TempSensor device that could be armed and disarmed and define a custom variable for that device that defines the trip temperature. Whenever the luup temp variable for that device is modified using the vera UI, you would send the updated trigger temp to the sensor node.
The advantage of this approach is that you can use your TempSensor to trigger scenes when armed (e.g. freezer door is closed) and the current temp exceeds the trigger temp akin to how motion sensors are used. In addition, it would act as a normal temp sensor reporting the current temperature to your vera that you could plot over time to check your freezer performance/efficiency.