You can control who can see the tabs using CB Privacy, but there's no functionality to output a message like you're wanting. The tab just flat out wouldn't output at all. CB Conditional can also used to condition tabs display. Both can also condition field displays. You could use a custom tab visible only to public users (conditioned using CB Conditional) that displays your message while CB Privacy or CB Conditional protects the normal tab so only registered users can access it.

Don't understand what you mean by link the tab to content. Once you create the tab within CB > Tab Management you need to add fields to it within CB > Field Management otherwise it's empty.