I create families in CAS and use a different skintone for each sim. Then I name each sim by their skintone for easy reference once I get to Simpe.  For example, I make the skinner family, I name them Fmlouislt (Fashion Model Louis light) or BGlouistan (booty girl louis tan), and I put them in the family bin.  I don;t delete them, in case I might need to use them later, or I want to change someone to something else later.  I then go to Simpe and find the sim with the skintone I want to use ( neighborhood browser, sim browser, find your sim)  I then go to the more section on the menu for sim information and then sim DNA.  I find the long number for the skintone and highlight it and then control c to copy the number.  I then find the sim I want to change the skintone of and open their DNA.  I highlight their existing skintone and then do a control v to overwrite their skintone with the desired skintone that I have copied.  Make sure you click on the commit button.  You can do several sims one right after the other. I usually plan ahead so that I don't have to go back and forth so much.  I will decide ahead of time which sims I want to change to what skintones and then I don't have to change the copied skintone so often.  Make sure to save once you have made all of the changes that you want and when you go into your game they will have the new skintone and the related bodyshape, even when naked.  You can then summon them to any household and use the wardrobe changer to change their clothes or use a mirror or the plastic surgery reward object to change appearance.  It's not as complicated as it sounds and I can change many sims quickly using this method.  If you have many bodyshapes, you could use the shape as the last name, like the bootygirl family and name the different sims by their skintone.  I hope this helps, and I found one person that did something similar in this thread, but nobody that had my same method.  It works well for me.