Press 1, 2 or 3 to switch layouts. The layouts are nearly empty so the change of layout is instant but if you have multiple objects the loading works exactly as you'd expect it to; once the layout loading is finished it'll change layouts.
You store the name of the layout you want to jump to in a global variable. The loading screen has only one event that jumps to the layout stated by the variable. Every time you switch layouts you'll do it the same way: set the variable and jump to the loading screen layout.