quantj is correct, at least from my understanding - no way to directly set the layer through a drop-down menu, though this should be included as one of the options in a dynamic component, IMHO - could be a powerful way to manipulate the model.
As for now, a good work-around would be to create a sub-sub component of the item in question that you want to change the geometry on. Then put that sub-sub component into two ‘container’ components, one on each of the two layers - a sub-component who’s only purpose is to 1) live on a certain layer 2) provide a window to that sub-sub component, and to pass the properties along to it. 3) go hidden/not-hidden based on menu chosen in the main component options dialog. then you’re not adding additional geometry (is that correct? We’re using the sub-sub component, twice, but it’s the same component (not ‘unique’) so only counts against polygons/model size once. If i’m wrong here let me know, oh SU gurus). Then when you write you sub-sub component, make sure you use the =parent!Attribute (Attribute being LenX, X, Y, RotZ, etc) instead of referencing the container component itself. That will allow your sub-sub component to inherit properties from whichever sub-component container it’s parked in, without throwing an error.
Hope this helps!