How can I add another action button within the approval process?

My Fire Chief has just asked for a Hold button.  Currently, the process I'm building for him has just Approve and Reject.  His idea for the hold button would be that, if he doesn't want to approve it yet but he wants the applicant to know there's a reason for a hold, then (if I program this right) he could hit Hold after putting a comment about the situation in the comment box and the process would take that comment and email the applicant with a message that says, "Please note, we have received your application, however, your permit is on hold for the following reason:  (Fire Chief's comment)".

So, can I just change the Submit button to say "hold"?  (if so, how)

Or can I build an entirely new button? (if so, how)  I couldn't find any instructions in the Help files.