It needs a little modification
//In the symbol definition of layout1200,layout800, add a creationComplete event and add the following line:
var parent = sym.getParentSymbol().getParentSymbol();
parent.setVariable("currentSymbol", sym);
//Then, in your Stage, you can access the symbol by doing this:
var mySymbol = sym.getVariable("currentSymbol");
mySymbol.play("myLabel");