Looking at the change in the master branch of VTK, it looks like the const correctness change is available. See https://github.com/Kitware/VTK/blame/master/Common/Core/vtkLookupTable.cxx#L740
If we backport the commit onto the older fork of VTK based of VTK7. See https://github.com/Slicer/VTK/tree/slicer-v7.1.0-2016-09-23-3b13ad9
We wouldn’t have to make the code in Slicer more complex