customizing the delivered 'notify author' email that comes from dispositions

I have grown leaps and bounds with my URM knowledge since my last posting, but I am still running into some things that throw me for a loop. This is one of them. I created a disposition, and the action I selected was Notify Author. When the author gets the email notification from the disposition, it is very generic. I need to be able to customize the email, based on the disposition step. Another words, if the step is 'when expired' do ' notify author’ I would like the subject line of the email to say ' Content expiration notice'. If