I would starte by reviewing the Customizing email content knowledge base. In the JIRA_INSTALL/WEB-INF/classes/templates/email/subject folder you will find the velocity templates for the subjects in JIRA. These are the templates used to generate the subject of the emails. The templates are named after the event that will trigger the email. Using that in conjunction with the Velocity documentation you should be able to achieve your goals.
In addition you may also want to try the Outgoing Email Template Editor for JIRA by AtlaZon. This is a server only add-on but it provides a GUI interface to the velociy templates.
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