How I fixed Demonica's neckseam (screenshots)

Maybe you'll find this useful if you're into Skyrim modding or find yourself in a similar situation when re-baking isn't an option (or doesn't provide the results you want).

In this case, I've used re-baked vanilla normalmaps and cut out half of it, then projected this half on each mesh. As you can see, I also filled half of the head's texture with white color so it's easier for me to locate the same spot (since the head model is the same) on the same head model with a different body.

So, here's the simple thing:

And then I did this for each (Red, Green, Blue) channel on both models: