So, I'm sure anyone with experience with 3D modeling and nif texturing already knows (and much better than I) about the lighting/shadowing of meshes of the character model. After researching it myself recently though, I have an, I think, interesting idea for how the issue with the separated lighting of the head and body meshes could be solved. We all know about the neck seam, but the visible textures are really only a small part of that problem, where hidden to most amateurs the real problem lies in the fact that the shadow for the head stops short at the point where its mesh ends, creating a very obvious line in any lighting condition where the light source is above the character. Even if you spend the effort to adjust the visible textures on the headhuman.dss file around the neck, and adjust your face data on your characters to a default skintone and eliminate or greatly reduce the seam in "good" lighting conditions, you will still get a terrible seam caused by this shadow problem.

I think I've come up with a potential solution, but I'd love to hear from some more expert modeling folks on it. I'm only an amateur with Blender, Gimp, and Nifskope, so doing the following would be an extreme challenge for me, so some assessment of if it is a total waste of time or not, and some pointers on how to proceed would be beneficial:

Step 1: copy the vertices from the headhuman.nif to their relative position into the body mesh with the with the appropriate bone weighting but remove the original texture material property and the texture property from the head verticies. The meshes are now joined as a 1 mat 1 for export as a single mesh nif later

Step 2: we don't want the "head" copy to have visible textures obviously, so the next step would be to change the body texture main dds file to incorporate both the original texture as well as the appropriately placed "empty" space where the head texture would be in this new unified mesh.

Step 3: the key to the whole idea, we DO want the normal to have texture on the head, so copy the normal map texture from the head file and put it into place correctly in the newly sized normal map counterpart to our larger texture file for the combined body and head mesh in step 2.

With all of this together, what I'm assuming would happen is you would have an "invisible head mesh" with regards to colored texture that is always attached to the body mesh occupying the same space as the actual head mesh. The normal map from this portion of the mesh would still cast its shadow on the rest of the mesh even though its color texture is invisible. Yes, the facegen data would be different and the shadows a little off, and if you're wearing various helmets there might be problems, but if there is any merit at all to this idea, I think it is worth using because what I'd imagine would be only slightly wonky shadows there are a great improvement over the extreme wonkyness of the way the shadow stops short at the seam now. Also, most NPCs that you actually get to look at closely don't wear helmets, so any strangeness there is a more minimal impact on the game than the current set up...

Any comments about this idea would be appreciated. As I said, I'm an amateur so, the hardest part for me is figuring out how to change the dimensions of the texture files to incorporate the head and body size together and have everything line up correctly still on the mesh... at a loss currently how to do it.