The "CreaseSplitting" command is in a V4 Labs plug-in called SurfaceCreases.rhp. This is an update to the Rhino V3 plug-in and command. This command will be built into Rhino V5. V3 users requested that we provide a V4 version of this plug-in and command.
The CreaseSplitting command line looks like
Split creased surfaces into smooth polysurfaces ( SplitAlongCreases=Yes/No )
If SplitAlongCreases=Yes, then when Rhino surface creation commands like ExtrudeCrv create a surface with a crease, the result will be a polysurface that has edges at creases.
If SplitAlongCreases=No, then when Rhino surface creation commands like ExtrudeCrv create a surface with a crease, the result will be a single surface with creases.
1. If you have not installed the latest Microsoft runtime libraries, then download and install them by clicking on the the link http://en.wiki.mcneel.com/content/upload/files/vcredist_x86.exe
2. Download the plug-in file SurfaceCreases.rhp to a folder on your computer.
3. From Windows Explorer, double-click on the SurfaceCreases.rhp file to install it as a Rhino 4.0 plug-in.