To customize a library element, please follow this procedure:
1 - Open the library catalog, and copy the handrail library to a user folder (drag and drop in the folder tree).
2 - Right click on the library and select "Open in shell", and open the .max file
3 - Select the railclone object, select each segment and extract the geometry as instance (right most button, below list): http://www.itoosoft.com/railclone/reference/refsegments.php
4 - Modify the segments, editiong faces or geometry. RailClone object will change automatically.
5 - Delete extracted instance and save .max
6 - Change thumbsnails and descriptions for the new item.
About additional styles we are preparing new libraries of styles that will be included on following plugins releases. If you will like that we add some specific elements or categories we are open to any suggestions.