Can content variables for Automated email message be modified?

Can content variables for Automated email message be modified?

We have some additional custom lines added to certain ticket type with our Service Catalog. These lines would be helpful to return in the automated email, to the requestor, when a ticket is closed.
 
In the Notification Rules, Customize Template screen, is there a way that we can get these additional fields/lines to be available in the content variables scroll box? Or can they be referenced and included by adding the appropriate '$variable' to the content message?
 
An even better solution would be if there were a way to link specific Catalog requests with a unique template when the notification rule is invoked.

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