My Tivo Bolt died a couple weeks ago. Weaknees said the motherboard had died, a repair wasn't feasible, and the hard drive was not transferable. So I bought a new Edge from them.
I transferred the cablecard (M card) that had been in the Bolt to the new Edge. I couldn't get the cablecard activated by Xfinity using their website, app, or by going to their retail store. They sent out a "professional technician" who had never heard of Tivo or of cablecards. His supervisor told him it wasn't possible.
After some research I made a post on reddit in r/Comcast_Xfinity. Comcast's agent there was able to get the cablecard activated for me. Now you know.