One thing I know is possible is usage of MC Command Center to copy and paste likeness and outfits to another guy (I don't know about personality traits but if you're using MC Command Center, you can easily change personality traits around with cas.fulledit). There's also the cloning machine where you can clone a guy, move him out to his own household, rename him in CAS, and then save him to gallery but that requires one of your Sims being a scientist to use.
I also know you could manage traits and delete memories from there, forget all your skills and forget careers, relationships do start clean if you start up a new save even with a Sim who has everything done.
