def alter(m_wfid, m_error, m_action, msg, tracker)

      case tracker['msg'].delete('_alter')
        when 'merge' then msg.merge!(tracker['msg'])
        #else ...
      end
    end
def alter(m_wfid, m_error, m_action, msg, tracker)

      case tracker['msg'].delete('_alter')
        when 'merge' then msg.merge!(tracker['msg'])
        #else ...
      end
    end
Alters the msg, only called in "pre" mode.