I have to agree with this comment. I’d probably just set up the router regardless (probably in WiFi AP mode) and not worry about it too much. No one reads the terms and conditions anyway. If someone comes to actually enforce the thing I’d obviously take it down. Hide the ssid if you want to.

As others mentioned, there are ways to also hide traffic behind a single device, maybe connecting to a VPN on the router level would help with this?

Back when I was in uni I had terrible wired Internet so I’d try everything. At one point I was using a jailbroken iPhone to share its 4g connection without having to pay extra to the wireless ISP (basically data plan was unlimited but tethering wasn’t). It worked fine, I could use my data on any of the devices over wifi but it was barely faster than the wired network and it was a lot of hassle so I gave it up.