It's simple: if you're a person that's supposed to be shutting down that computer, you'll be able to. If you're encountering the message, you're using the wrong account, or you're the wrong person to be doing that. Switch accounts, or call up the right person.

Non-privileged users of such systems shouldn't care about updates or whatnot. They're there to do their work not mess with the system managed by someone else.

Then you su to a privileged account, or something.

Allowing a random passerby to access the update settings of the kiosk computer is a lot more stupid, and also insecure.