Modding Request - A layering mod

Hi, I'm pretty sure none exists and I feel sure one would have been created by now if it were possible, but could some kind soul explain to me why there's no skin details layering mod in S4?  I haven't played Sims 3 in about a year and a half, but I'm about 90% sure you could do this with NRAAS's MasterController.  I'm just truly curious as to why this can't be done in S4.

Thank you in advance, and please don't be afraid to dumb down your explanation - I know nothing about modding and I'm not particularly smart either.   And of course if there IS a mod like this, PLEASE let me know!  It would make my year.  Thanks.