Adding additional template items to the template. There are a few places to edit.

plugins/cerberusweb.core/api/listeners.classes.php around line 530.
and
api/app/Parser.php around line 671

Code from listeners.classes.php but both code is similar.

CerberusMail::sendTicketMessage(array(
'ticket_id' => $ticket->id,
'message_id' => $ticket->first_message_id,
'content' => str_replace(
array('#ticket_id#', '#mask#','#subject#','#timestamp#','#sender#','#sender_first#','#orig_body#'),
array($ticket->id, $ticket->mask, $ticket->subject, date('r'), $ticket_sender, $ticket_sender_first, ltrim($ticket_body)),
$group_settings[$ticket->team_id][DAO_GroupSettings::SETTING_CLOSE_REPLY]
),
'is_autoreply' => false,
'dont_keep_copy' => true
));