For example, you might want to add decals to the universal head - more scars, facepaint, eyebrows, beards, bullet holes, etc.
While not integrated with the modders workshop, this is relatively simple modding process.
Starting with a making a new addon folder, it needs some other folders created folders:
I'm making a red cross to go on a guys face, so I created these folders:
(red cross 1.jpg)
In the Male01 folder i had created, I made a new file called "Universal Head.bodypart" (note - I made it as a txt file, and changed the extension to .bodypart)
It's contents are as follows:
<partsCovered class="enum-set" enum-type="mscope.things.BodyPart$Category">HEAD</partsCovered>
<name>Red Cross 1</name>
<diffuseColor>1.0 1.0 1.0 1.0</diffuseColor>
The interesting bit is between the <decals></decals> section - you can have multiple decals, each within it's own <material></material> tags.
I also made an image, a red cross on a transparent background, as a .png (you can also use .dds files). I put this in my Heads/RedCross folder, and then put the relative path from the .bodypart to the image, in the entry for the diffuse map.
I set the name, in the material, to something of my choice 'Red Cross 1', and I created a .jpg thumbnail with that name, and the .jpg extension, and put that in the Heads/thumbs folder.
I also set which decal group my new decal should appear in.
I then went to the modders workshop, and published my new addon, and then tried it out.