If the Aesthetician can add or remove the horns that comes with some Au Ra hairstyles (esp. some of the male hairstyles have horns coming out from all over their heads) and add or remove the scales of my face and also remove or change the color of the limbal rings (or scars for some other races), he could possibly learn how to change my eye and skin color as well.

So, lore-wise it actually makes no sense that he can't. xD