Is it possible to disable @mention of a public group in any post or comment by regular users ?
Only particular profiles should be able to @mention the public group name.
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There's also a new type of group called Broadcast Groups that restricts group posts and @mentions to the group owner and group managers. It's being piloted in Winter '16 and will be generally available in Spring '16.
It doesn't have profile-based restrictions, although you could write some code to allow all users with a given profile to become group managers.