My goal is to allow these anime NPR custom normals to be kept consistent when using shape keys to create expressions. The normals are setup to give a very specific shading results and the deformation changes to the normals kills it.
Here is an example. The top model is the hand edited normals and the bottom is how they fall apart once a shape key is applied.
I myself would actually use data transfer modifiers to keep things procedural and have more control. Also since I don’t use shape keys I rely more on bone rigs the armature deformations would also kill the custom normals.
But many NPR users use shape keys for their face rig so I want the custom normals not to fall apart.