[Daniel]

You will need to make a plugin

Product: vBulletin
Name: Only unregistered sees link in navbar
Hook location: global_state_check

if($vbulletin->userinfo['usergroupid'] == 1)
{
$show['unregistered'] = true;
}else{
$show['unregistered'] = false;
}

Plugin is Active: Yes

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Now go back to your Navigation Manager
Edit the link you want
In show permission name type "unregistered" (no quotes)

Note for other people: It doesn't have to be unregistered or usergroupid 1. Customize it for admins (usergroupid 6), registered users (usergroupid 2), etc.