So worked on an issue today where we wanted to update the TargetAddress of a Mail-Enabled contact object on Export.  Our goal was to use the Mail-NickName and the msExchOriginatingForest attributes to combine and make the TargetAddress.  Here are the steps that I put together to accomplish the task.

How to customize targetAddress attribute on Export: http://social.technet.microsoft.com/wiki/contents/articles/how-to-customize-targetaddress-on-export-attribute-flow.aspx