Last night I was attempting to create a package file to make default alien skin replacement. I built it from scratch from a tutorial on MTS2, and used Maxis S1 skintones for testing. The package file worked, but I noticed that the adult male skin did not appear to change when I used the testing cheat to make him fit. I tested the teen male too and saw the same thing. After a replacing the fit, normal, and fat textures in my default alien skin replacement file with different skin tone colors, I discovered that the game was using the normal body texture for all fitness states. The game uses the correct mesh, but not the correct texture.
To check and see whether this was a mistake on my part, or a Maxian bug, I downloaded a few other default alien replacement skins from MTS2 and looked at them in SimPE. One didn't even have textures for any of the fit or fat bodies. It only had replacements for the normal body textures for both genders, teen through elder. (Seems this is a known bug.) The others did include textures for fit and fat bodies, but in my testing the game still only used the normal body texture for all fitness states.
It turns out that I've already stumbled across a work around. If you create a replacement pollination technican with a custom skin tone, the game will use the correct texture on each fitness state. I used fwiffo's
Multi-PT Kit to create a replacement PT hack back in December. For that hack I had created a custom alien skin based off the Maxis S1 skin tone recolored green. The skin is fairly close to the Maxis alien skin, just a slightly deeper green and not quite as bright. After some testing (by replacing some of the textures in my custom skin package file) it looks like the game is using the correct fit and fat textures.
You can download my PT replacement hack
here. The hack file comes with 2 sims: Maxis' Pollination Technician (from PatchesSim2's simpage) and my avatar sim both of whom use my custom alien skin tone and custom black eyes. They share pollination duties 50/50. There are 2 other versions of the hack file available on that thread too. One makes PT the sole pollinator, and the other makes my avatar sim the sole pollinator.
This hack is not a replacement of the default alien skin. It won't affect aliens already born in the game. It will use the custom sims I created as the new alien fathers and use their skin, eye color, and face for the alien genetics.
This hack won't take affect until your neighborhood has had one alien birth. The first alien birth always seems to use Maxis' original PT, alien skin, and alien eyes. After that, future abductions should be handled by the hack. The Maxis alien eyes seem to be linked to the alien skin, I don't think you'll ever see them passed down independently of the skin. But with this hack, and the custom black eyes, they will. The S4 skin tone actually looks pretty good with solid black eyes (IMO).
I wish I had know this before I spend a few hours last night in SimPE creating an default alien skin replacement package file. Oh well, at least I picked up a SimPE skill point.