I edit my townies all the time, (outfits, name, traits), I also use the occasional saved or gallery household as townies.
How I add households as townies:
Click on an empty lot and select the option in the lower right to add or create a household
Now add your sims in CAS, save the household
Click on the empty lot you used for the household and evict them
Mark the household as unplayed
I keep the Pebble Burrow lot empty in all my games so always use it, you can use a lot with a house on it if you don't have any empty ones, the computer is just faster with no build on it, is all.
