We don’t have any new API function in this area. However, as shown in Hiding Object from html - #2 by wojtek you can use the existing API functions underlying the Switch Objects extension to switch objects from an external interface.
Unfortunately, this is not possible, because the Shapespark viewer doesn’t support dynamic loading of 3D objects. All the objects must already be in the scene.
Yes, if the switchable objects occupy the same space, it’s recommended to bake them with “Isolate shadows” option enabled. Otherwise, the objects would shadow one another, or leave shadows that don’t match the scene.