Change a M5 main router to a new M9
I need to add a couple more routers to my Deco network. My original network is three M5s and it is operating fine except I need to expand it with a couple more routers. I have ordered three new M9s and I understand it is best to make the main router a higher model - in my case my main router s/b a M9. So, here's my question. If I first simply add one M9 and get it operating in the mesh, could I then connect the M9 to the modem via Ethernet at the same time the original main router is still connected? My thought is to then make the new M9 the main and then disconnect the original main from the modem, but leaving it on the network. Is this doable?