Most objects in Vectorworks documents are plug-in objects, or High Level Objects. Various parameters of these objects are controllable through the Object Info Palette (OIP), however they cannot be modified directly with the 3D reshape tool, used in Add or Subtract Solids operations, or customized any further than the OIP allows.
One option is to Ungroup these objects, which will reduce them into their basic components.
Whether you get 2D or 3D geometry when you ungroup the object is determined by what view you're currently in. Top/Plan view will yeild only 2D information, but the Top, Front, Isometric and other views will result in 3D information.
NOTE: Which this is a useful procedure for custom drafting, you cannot recombine the ungrouped objects back into a plugin object after you have ungrouped. This means that you should control and modify the object as much as possible with the OIP first and then ungroup to perform further modifications.
Edited by JimW