Earlier quoted context omitted.
Then they'd need to announce that to all of the users of their DNS service. You tell me how to do that.
They'd do it the same way every web service since the beginning of the internet has done it. "By using service X you are agreeing to be bound by the terms located at .... "
That's why whenever companies change their ToS you get email/notifications/actual mail informing you of the changes.
You can't do that for DNS.