It is possible to edit a Sim in The Sims 3 after creating them in CAS by using cheats, having exactly the same options had when they were created.
  1. Press Ctrl+Shift+C to bring up the cheat console.
  2. Type in the bar that appears on top of the screen "testingcheatsenabled true" (without the quotations).
  3. Shift-click the Sim that requires editing and select "Edit in CAS".
  4. Make whatever changes are desired.
  5. Make sure to save your changes.
  6. Before closing the game, make sure to bring up the cheat console again and type "testingcheatsenabled false" (without quotations).

Note: does not always work when changing life states, i.e. Human to Anything works, but not Anything to Human or Anything to Anything. Untested for Genies.

Also note that if you do this after you build up the Martial Arts Skill in the World Adventures expansion, the Sim will revert back to the original Sim whenever they are in their martial arts uniform(s). However, they will change back to the new Sim when changed into one of their other outfits.