Bypass modem activation?

I have two modems i alternate them night and day. Don’t ask why but I just have to do it …

It always asks to activate my modem every time I swap it and sometimes it’s under maintenence and I can’t use the internet until i get the other modem back.

Is there anyway to bypass this? called my ISP they said I’d need to pay for two internet services.

If anyone of you could help me out with this it would be great.