I am trying to do the following. I import an FBX with several meshes, all with custom normals. Some of the meshes have normals pointing the wrong way. How can I flip the normals (ie. rotate exactly 180°, or scale with -1), without destroying the very valuable custom normals orientation?
If I use the CTRL-N command, or if i click on “Flip Normals” under “Tools–> Shading/UVs”, then Blender not only flips the normals, but recalculates them (based on the face orientations), leading to ugly shading artifacts.