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I've been experimenting with just face mesh swaps, using the original game's face tints, default installed body/face textures and no esp, the results are actually pretty good IMHO. This is Svana Far-Shield (left) and Frabbi, with face meshes taken from Bijin NPCs and hair meshes/textures from KS Hairdos. You need to change the NPC weight using the console to avoid neck seams, but otherwise this method can work pretty well if you need a no-esp mod I think.