It wasn't clear what was being used or how it is set up. Just switching PVRs should not be an issue. They are essentially independent from the internet for watching and recording cable TV. I doubt that any changes would be required for the modem or network. It sounds like the Google Mesh system is capable of automatic configuration and adjusts to work with the existing modem configuration. Extra services such as remotely programming the TiVo or viewing recorded programming remotely would likely use wifi but it shouldn't need anything special.