I model vehicles and when I split front bumpers from sides and rears I replace the edge vertex normals to match the connected version. When I apply a surface appearance object to add paint shine it ignores said normals (I only apply a greyscale texture for roughness and metalness map)
Surface appearance with same textures for roughness and metalness on all 3 meshes
Mesh parts with no surface appearance but with reflectance to highlight vertex normals on all 3 parts
I feel like if the normals section does not have a texture asset assigned to it, it should retain the existing mesh properties.