Attempting to Editor-script changing the shader in ProceduralMaterials

I would expect the code below to work. And, when I debug it, I can watch all of the values change correctly. But, afterwards the assets in the Editor show no change.

Any clues as to what I'm missing?

Code (CSharp):

1.         SubstanceImporter importer = AssetImporter.GetAtPath("assets/bundled/materials/commandcenter1.sbsar") as SubstanceImporter;
2.         Shader shader = Shader.Find("PbrNormOcc");
3.         var mats = importer.GetMaterials();
4.         foreach(var mat in mats)
5.             mat.shader = shader;
6.         importer.SaveAndReimport();