As in the title, for example, something that makes you able to enter CAS through mirrors, not just edit hair; or a beauty salon where you can change skin tone and facial appearance etc.

If you have Generations (I think) your Sim can get plastic surgery but I don't think you can change their skintone. I don't use Generations a lot, so I can't remember off the top of my head.

And I'm sure you don't want to go the cheating route-for whatever reason-but you are aware that the built-in TestingCheatsEnabled true cheat allows you to do this by right clicking on the offending Sim? There is no need for external mods to do that.

Yes I'm aware of the TestingCheatsEnabled method but I'm looking for a more immersive way of changing a Sim's appearance