Don't you have problems with "Tweaks"->"Genetically modify Active Sim" option?
I can set everything perfect except sims's weight and muscle. I set a fatty sim to maximum fat and maximum muscle and in the game after a minute the sim looked like exactly before I changed her look.
I changed her look 4 times, she changed back in game 4 times.. This happened with other sims too.
I think that option doesn't work anymore..