You’ll need SkinTexMod for this to work, it’s an overlay so it won’t screw up your customization. I don’t plan on making an actual tattoo in the body tattoo entries, because the game limits them to 1024×1024 max, that looks horrible for such a small tattoo.
I made two versions to use, dds for people with small VRAM amounts like me, and tga for people with tons. I also uploaded the psd source, in case you want to edit it (change its color or whatever). Remember to invert if you save as dds.