I created a master object library file from which concrete projects can link in the objects needed for our scenes. The goal was that if we needed to touch up an object we could then do so in the master object library file and re-render from scenes in project files. The snag we ran into is that a couple of the master objects are used for two purposes: 1) Cast shadows but not be visible to the camera in one scene, and 2) Be visible to the camera in another scene.
So we were surprised to find that Ray Visibility options are grayed out on linked objects.
If it's not possible to change the options, we'll need to come up with a different approach.