Alien question

[Alex]

I'm just wondering if there's a hidden variable that makes a sim a "true" alien. Whatever it is, I'd like to fix the pre-made aliens in Strangetown, who shouldn't be able to overheat (but they do as they are normal CAS sims with Alien genes slapped on top).

[Milhouse Trixibelle Saltfucker III]

If I recall correctly, the game doesn't prevent aliens from overheating at all, since there's no difference between them and other sims besides skintone. It's just Prima Guide L&P. Check the warmth thread in the War Room for more.