The current Service Catalog notification emails that are sent out via Event-Rule-Actions have limited configuration options.
When sending out enterprise-wide emails, there are business / organizational requirements that apply. To comply with standards and regulations, application owners will need to format the system email notifications (Header, body, footer, etc.) and embbed image file(s), additional hyperlinks, highlight text, format text, add/remove entire sections that typically appear within the standard notification email.
Currently, outside of modifying the Message value in each of the actions at the Event-Rule-Action level, we do not know how to do something like this. If there is a way to do all of the above already, including it in documentation would be of great value to customers.