Yes, you can repurpose an old router as a modem.
Yes, you can repurpose an old router as a modem.
It depends on whether your ISP offers a multi-service provider setup. For Verizon, using MOCA and lacking a coax connection might prevent connectivity. Could you share the router model you're considering?
Modems are designed for specific internet connections. There aren't universal solutions that fit every type. Since you use DSL, VDSL, DSL+, fiber, LTE and satellite, each service behaves uniquely.