(If there is no modpack present, that means one has not yet been updated post-dawntrail)

Use a photo editing software to layer the cutout on top of your body base.
Using a cutout gives you the freedom to layer tattoos, scales, and skin textures!

[How to] For importing textures into Penumbra.
Loose file editing: https://reniguide.carrd.co/#

[Bases] For Photoshop Masterfiles and body textures.
!NSFW! (fem) Bibo+: https://www.xivmodarchive.com/modid/29029
!NSFW! (masc) TBSE: https://aetherlink.app/mods/6994949803713265664

Have fun :)
-Juliet