Thanks for the question. We've been having the same conversation here lately where libraries only work correctly if instancing is turned off for particular renderers. As a result, future versions of RailClone will include a functions that can be called to disable instancing if the current renderer doesn't support a feature. It will use the following syntax that should be added to the library's index.xml.
<maxscript script='@RC_disableInstancing "$(RENDERER)" "corona";' execute_on="item_select"/>
Where corona is the renderer for which you would like instancing disabled. Other options include mentalray, and vray.
If you would like to disable instancing for multiple renderers, just add them separated by a space, e.g.
<maxscript script='@RC_disableInstancing "$(RENDERER)" "corona mentalray";' execute_on="item_select"/>
I'm afraid this won't work quite yet, but the next builds of RailClone 3 will include the function to which this line refers, so you can start using it then.
I hope that helps, please let me know if you have any further questions.