No there is no way to restrict anyone from creating a new login and password. The point of this particular subscription is to have one local terminal that anyone with access to the terminal can use. Other subscriptions allow only one user access but in exchange offers that one user through a BB Anywhere addon (at no extra charge) can access the terminal from anywhere. So, I do not see your point why you would want to restrict anyone from accessing the terminal in your library. Creating new logins does not add any overhead, not memory wise, not CPU wise, and not hard drive disk space wise. Its not like a windows user where the machine sets up an entirely new path with tons of files and user configs. All configs of a BB users are saved and kept on the BB servers. I share this information because I know someone who works at BB.
If illegal content is disseminated over BB-chat or messages then you would want to talk to BB to get the users information so that you can follow up with the user yourself, but you would need to be an account authorized person to do so.