@ikaz1106 

If you want to just keep using your existing router with the Deco, set the Deco operation mode to Access Point. 

The Deco will still provide you a mesh network, but will just work as AP units and not a router. 

I would recommend renaming the Deco to be the same network name and password of your router, and just disable the Wi-Fi on your ISP router. Leave the wireless coverage to the Deco.

Just to clarify, you must have at least one Deco wired to the ISP router.

@Tony  Similar setup, but need clarification. If 3 Decos are in use, just the one cabled to the router (with WiFi access point disabled) in access point mode? Or all three Decos in AP mode?

And it seems obvious, but I hate to assume: Can gig ethernet devices (PCs, printers, etc) be connected to all unused ports on all three Decos?

@edp 

Router mode or AP mode will apply to all nodes at once.

You can leave the Deco network in router mode if you still want to take advantage of all the available features. Running in AP Mode will get rid of most features as it no longer handles routing. 

As far as the other slave nodes, you can wire devices into those ports to get wired connectivity. You could also attach a switch if you want to expand the available LAN ports as well on a Deco.

@Tony OMG so glad I goofled this before manually changing SSID on 40+ smart bulbs/outlets/etc.  Yeah just disable the wifi capability on your dsl or cable modem or your own router and rename Deco SSID and WPA password to same the connected devices expect and they'll never know what happened other than now signal quality is in the 90+% not 11% lol