Generally I want to direct polygons along
custom split normals, or at least get them work in AN. Can it be done?
You can get access to loops normals using the following expression:
[loop.normal for loop in [obj.data.calc_normals_split(), obj].data.loops]
Which calculates the split normals data and returns the normals. To set vertex normals to a mesh, you can use the
setVertexNormals method, which take a single vector list representing the normals.