This is the first time I've ever tried to make anything on this site. I've always found myself feeding on the success of other's inventions, so please forgive me if this is rough around the edges.
Here is a patch which fixes the neck seams on navetsea's skin set, for the CBBE version ONLY. The altered textures were made using Texture Blender, and I haven't been able to fix the UNP version. I've done a few tests on one or two face models - most extensively, WSBP - and it should be able to fix any others. If anyone finds a combination that doesn't work, please let me know.

To install, make sure that navetsea's latest skin is installed [http://skyrim.nexusmods.com/mods/6554], then download the patch. Unzip to the Skyrim folder and overwrite.

Thanks to navetsea for his efforts on the skin mod.