Average vert normals between 2 child meshes?

How can this be done in Unity? I would do it in my modeling software, but FBX doesnt support it on export for skinned meshes. And importing the modeling software file itself still gets converted to FBX in the background of unity, so that wouldn’t work. SO, how can I do this in code(unityscript)? Should be coded into a Start function right?

Vector3 averagedNormal = (normal1 + normal2) / 2;