def update_application_key_label(display_code, new_display_code, text)
      @repaint_required = true
      labels = key_labels()
      raise "labels are nil !!!" unless labels
      labels.each_index do |ix|
        lab = labels[ix]
        next if lab.nil?
        if lab[0] == display_code
          labels[ix] = [new_display_code , text]
          $log.debug("updated #{labels[ix]}")
          return true
        end
      end
      return false
    end
def update_application_key_label(display_code, new_display_code, text)
      @repaint_required = true
      labels = key_labels()
      raise "labels are nil !!!" unless labels
      labels.each_index do |ix|
        lab = labels[ix]
        next if lab.nil?
        if lab[0] == display_code
          labels[ix] = [new_display_code , text]
          $log.debug("updated #{labels[ix]}")
          return true
        end
      end
      return false
    end
updates existing label with a new one.
 @return true if updated, else false
 @example update "C-x", "C-x", "Disable"