I will add a rule set I created to only allow twitter.com/McAfee, while other twitter calls are blocked. The rule basically simply allows twitter.com/McAfee but blocks all other calls to Social Media websites, by blocking this category. You need to ensure that it does not interfere with your existing URL filter setup, e.g. remove twitter or Social Media blocks from your existing policy, otherwise twitter will remain completely blocked.
Also the rule set requires SSL scanner. It won't do anything without SSL Scanner enabled.
Users in the AD Group "Access Twitter" can access twitter. All others are limited to twitter.com/McAfee.