Are we sure these packages are loading? I've tried injecting the default skins into a custom skin package, and the skin won't load. It won't cause the game to crash, but I don't get the option to use that skin in the CAS screen.
I HAVE been able to inject one custom skin into another custom skin package and get it to load, however. I then created a sim with that package for testing purposes.
What I find interesting is that if you create a sim with a custom skin and the delete it (the skin) the sim starts using the default skin you used to create the custom skin. Restore the package, and they use your new custom skin again. This indicates to me that somewhere in the .txtra file is a reference to the original skin, and that information gets passed along to the sim you create.
To test whether it is the file itself and not the package, I've injected a custom light skin tone into a custom dark skin package, and created 2 sims--a male who has the custom dark skin from the package, and a female whose custom light skin was "injected" into the custom dark skin package. My expectation is htat when I delete the custom package, the male will have dark skin and the female will have light skin. If this is what happens, the we can safely assume that what default skin was originally used to create the custom skin is encoded in the .txtra file. If both sims have dark skin, then that information is encoded somewhere in the package file (NOT the .txtra file.) If they both have light skin, the game probably just assigns a new skin to the sim.
But I haven't had a chance to finish this test. I'll keep everyone posted, if you like.

If the extra data is stored in the custom txtr file that would explain the extra data that is causing the crash, yes please test.

The way I tested to make sure the package is loading is I changed one of the txtr with a custom and checked both in game and bodyshop to see if the new one showed up and it did, I then changed that one back to a default txtr. This package file made up only of original skintone txtr files (about 9 mb) has been in my default directory for a long time now without a crash. They use original ID's, that's what it takes to get them to load. If I play with the custom skintone the game crashes after 30 minutes or so.

I did that one time. Placed some nude skins from the Downloads folder into another folder within to hold them temporarily. Ran the game.
The nude skin was fine until I had her 'plan outfit', she decided on going nude that day. When the selection was made, her nude skin defaulted to the Maxis nude skin.
I didn't think about it because I played for a while and I saved the game(just plain silly). I put the files back in that I removed and played. She still has the default nude skin to this day.

OK, when I deleted the custom dark with the custom light female injected into it and ran the game, both sims sported the default light skin. So evidently the game doesn't care what the base originally was--if the skin ain't there, your sim becomes caucasian.
Incidentally, even if you save the game with the custom skin missing, your sims will still show the custom skin again if you can restore it.

Is there like a big file with all the diferent skin tones? Like the one in the picture?