You can activate notifications on a per task base. Go into the task details and find the notifications tab, there are several rules you can activate for notifications. All notifications are disabled by default unless you used a workplan template where this has already been preset.
As far as I know they are not editable and you cannot create additional templates for task events. You could try to change the existing template directly in the database (should be knta_notif_type_messages), but I would not recommend that.