@MaxCattum 

In the deco app Click on More > WiFi Settings > Click on 2.4 GHz & GHz Network > Click on the name of your network > You should be able to change it now 

  @John_Ch 

Assuming both the Google Mesh and Deco Mesh networks are configured with the same SSID and password, and all wireless devices are set to connect using these credentials:

SSID = Cat  
Password = 12345

Devices will automatically connect to either of the routers based on signal strength and other factors. 

If we choose to keep the settings for the Google Mesh as above but change the Deco Mesh SSID to "Dog," then all devices will be directed to connect to the Google Mesh network by default.

To connect specific devices to the Deco Mesh network, you'll need to manually update each device’s Wi-Fi settings from "Cat" to "Dog," which may be time-consuming depending on the number of devices.

This approach works well unless a router fails. For instance, if the Deco Mesh units fail, you would need to reconfigure each device previously connected to "Dog" back to "Cat."

In my personal setup at home, I turn off the Wi-Fi on my primary router and let the Deco units serve as the router. If one Deco unit fails, I can simply designate a different Deco unit as the main node. With a new 2-pack, I can easily add a replacement by opening the box and integrating it into the existing network.