Template format of syslog event

Several years after the original post and I'm faced with a similar issue, but on 11.6 HF5. I need to modify the template to include the internalID statement below?

Original:

    template t_commontmpl {  
            template("<$PRI> $DATE local/$HOST $PRIORITY $MSG\n");
            template_escape(no);
    };

New:

    template t_commontmpl {  
            template("<$PRI> $DATE local/$HOST $PRIORITY $MSG\n");
            template_escape(no);
            internalID:xxxxxxxxxxxxxx\n";
    };

Does anyone know how to make this change using tmsh, since that is the suggesed way to do this according to the warning at the top of the file when attempting to vi /etc/syslog-ng/syslog-ng.conf directly?