that doesn't work, in order to do what you want, you need to get out an old gui and script i made. i as well wanted to be able to do misc things such as that dealing with the tab menu so i set out to do it, and i found a way. you have to create a client side object that references to the tab menu. the object will save to the playgui and all you have to do is trigger it, Control::setVisible(MyNewTabMenu, true);
Have fun.