Changing "Dear " when mass emailing candidates

Summary

Changing "Dear <<CANDIDATE_NAME>>" when mass emailing candidates

Content

Is it possible to change the <<CANDIDATE_NAME>> field when mass emailing candidates? For example, if I navigate to a specific requisition, view the requisition candidate list, select multiple candidates, then select, the Send Email button, the email screen that pops up automatically populates the text of the email with "Dear <<CANDIDATE_NAME>>". I have the option of selecting an email template to use. If I don't want to select an email template from the list, how can I change the <<CANDIDATE_NAME>> field to reflect the first name field only?