Can I reset a sims skill levels or reset the sims but have them look the same.?.

If you want to add a sim to a family with DNA or otherwise, it is best to do so through manage households in the world screen. That let's you add sims and even remove sims from a household. Newly created sims are fully editable in the cas session when they are added, even without the fulledit cheat. I don't think adding sims is possible if you go to cas from live mode with a dresser.