Oh absolutely, I used that trick once in order to use a router that I could configure over web interface instead of Over The Cloud With A Spyware Mobile App (aka Internet Of Shit).
Unfortunately my ISP smartened up to this and started cutting the line whenever I tried to use my router. Like, it would work for a while, then they'd shut off service, and it wouldn't work anymore (even if I removed my router) until I called them up and complained.
They would act oblivious like the problem was with my equipment. Every time I asked them why my internet stopped working they would say there was some problem with my hardware. The hardware was brand new and could not have been more fine; they were mistaken. It would also work perfectly when I actually had service; the issue was the ISP kept cutting it because they're petty bastards.
Eventually I gave up, which is probably what they wanted, but it's not like I'm suffering too badly with their equipment, even if I have to use a rooted phone in order to pry away all the spyware permissions from their stupid app.
They are a monopoly so I have no choice.