begin
  rttiContext := TRttiContext.Create; 
  rtype := rttiContext.GetType(TMenuItem);
  rField := rType.GetField('FOnChange');
if rField <> nil then
begin
     V := rField.GetValue(MainMenu1.Items);
     OldMenuItemChangeCode := TValueData(V).FAsMethod.Code;
     OldSelfData := TValuedata(V).FAsMethod.Data;
     TValueData(V).FAsMethod.Code := @TForm1.MenuItemChange;//菜单项目变化
     TValueData(V).FAsMethod.Data := self;
     rField.SetValue(self.MainMenu1.Items,v);
end;

procedure TForm1.MenuItemChange(Sender: TObject; Source: TMenuItem;
  Rebuild: Boolean);
var
  m: procedure(selfData: TObject;Sender: TObject; Source: TMenuItem;
  Rebuild: Boolean);
begin
if Assigned(OldMenuItemChangeCode) then
begin
    m := OldMenuItemChangeCode;
    m(OldSelfData,Sender,Source,Rebuild);
end;
  ShowMessage('菜单修改事件挂钩');
end;