The following example demonstrates reassigning an event.

procedure TForm .Button Click(Sender: TObject);
var
  Button2SavedEvent : TNotifyEvent;
  Button3SavedEvent : TNotifyEvent;
begin
 {Save the events}
  Button2SavedEvent := Button2.OnClick;
  Button3SavedEvent := Button3.OnClick;
 {Clear button 2's OnClick event}
  Button2.OnClick := nil;
 {Set button 3's OnClick to Button2's old OnClick Event}
  Button3.OnClick := Button2SavedEvent;
  { Do something here }
 {Take us back to the original events}
  Button2.OnClick := Button2SavedEvent;
  Button3.OnClick := Button3SavedEvent;
end;