Weird, I followed your steps to a T...even triple checked, and my changed sim is wearing the skin I gave her for dominant and recessive dna and not the custom one with tats...
Maybe it has something to do with the tat skin being a skin I converted from another skin?
Are you saying the skin did not change for the skin you orignally gave the sim?
Which method are you using?
The hack from sims graveyard or the SimPE manual method?
Regardless of the skin being converted, it should have it's own value so this doesn't happen.
Have you tried which a different skin just to test it out to see if it maybe a bug with the tattooed skin?