It might be difficult, considering these things are not bound to only one particular skin tone, but I’m also sure with enough proper recoloring (aka, don’t take white skin tones and darken them… that will make them grey), it can be done! I can also imagine that one could just edit over the existing skin tones, and then save them as one layer each, under a different name… But I don’t really know how the Episode Artists do their jobs or what programs they use! I’m only speaking as a digital artist myself, with my knowledge of how layering works.
The only problem with having things like skin conditions is that people may use them so much in their stories that it doesn’t actually seem as rare as it actually is. I still think it’s an awesome idea though!