We'll now make a mod that alters the physical appearance of a game character. We will work with a NpcAppearanceStats file. This is not a Unity file, but one I made myself. If you want to know more about this type of file, check this article. For the moment, this file will only affect the overall size, and the boob and butt proportions. I can't promise more right now, but I'm always open to hearing your feedback and consider every suggestion, in case there's something else you think would be a good thing to modify with this method.
The min and max scale will modify the total scale of a game character, but will maintain realistic a head proportion.
Right click on any empty space in the Project window, and go to Create > Game Stats > Npc Appearance Stats.
Rename the newly created file if you want, though it's not necessary at all.
I'm going to modify the min and max boob sizes for this example. Let's make some tig bitties!
Select the child GameObject of the ModelContainer, and in the Appearance Stats, under "Other", drag and drop the NpcAppearanceStats file we edited.
Note: even though the image shows "Needs Hair" and "Needs Eyes" fields unchecked, you should leave yours checked for now.
Select your ModelContainer in the Hierarchy window, and in the Inspector window, open the "Overrides" dropdown. There, look for a button that says "Apply All" in the bottom-right.
This will "save" the changes you made to your ModelContainer prefab.
After that, go to AssetBundleBuilder > Build, and wait for your mod to compile.
If you put the mod file in StreamingAssets > models (in the game directory), you'll see the changes in whatever character you apply the mod.