LayoutMgr.setDefaultLayout (alias)
Set the layout with the alias passed as argument to the default site layout

Sourcecode in LayoutMgr/objectFunctions.js:
1:   function setDefaultLayout(alias) {
2:      var l = this.get(alias);
3:      if (l && this._parent.layout != l)
4:         this._parent.layout = l;
5:      return;
6:   }