There are several ways you can do this.  The first is to see if the object may be split in the  polymesh options box.  Sometimes 3D/Obj objects come in one color/texture but they are will split in the options box.   For instance the dystopia modules will split into 20 some materials.  You can split those off.   You can save the models (if allowed) as 3DS or OBJ. objects and export them.  I'm not too familiar with Maya but I think you should be able to import Obj./3DS  files.  You can also take a program such as Wings 3D and import the models and cut and whack to your hearts content.  (Also it gives you ideas how to build things).  You can also assign materials to the mesh.  Which when the object is imported into Vue can be assigned with Vue materials or edited.  

Another free program is Blender.

Note: some objects available from Cornacopia are locked and cannot be exported as 3DS/OBJ files from Vue.

Hope this helps a little.