Selecting Mesh > Unsmooth lets you unsubdivide any Catmull-Clark smoothed, high resolution mesh. You can set the number of subdivision levels to recreate in the Unsmooth Options or polySmooth node. Unsmoothing can be useful for creating low resolution versions of meshes that have been smoothed and subdivided during the sculpting process.
Workaround: Separate the mesh into separate shells and then run Unsmooth on each piece independently.
To unsmooth a mesh
Adjust division levels of an unsmoothed mesh
Model provided by: Christoph Schädl