Cloning a sim has been explained before.

1. BACK UP the Neighborhood! If something goes wrong you will need to restore the backup to fix it. Please don't skip this step.

2. Open the neighborhood with the neighborhood browser

3. Find Sim Surgery.   I usually find it as a handy button along the top labeled Sim Surgery, which can be added by right clicking the tool bar and choosing "add" if you don't see it. It's also under one of the menus, but I forgot which one.

4. click the archetype box and browse to the sim you want cloned. depending on how long it's been since the thumbnail updated it might look like the wrong age, but it's still the right sim.

5. Click "export to bodyshop"

This will give you a sim in bodyshop which you can then Create a Sim with and give the personality points, etc.

If you want the skills as well, you can use the sim blender, Insiminator (no longer recommended as the creator no longer supports it.) or SimPE to add those.

As for making a no character data sim playable, it requires giving that sim data. This is an even better way to accidentally destroy your game if something goes wrong.

I googled and found the the steps, to which I would add one before everything else: MAKE A BACKUP!!!!

In your case, I would also recommend practicing with cloning before trying something more complex.

Resurrecting Sims with no character data

A summary of the tutorial by Celesta92059

1. Create or download a clone of the Sim you want to resurrect.
2. Open the clone in SimPE and open the Character File.
3. Select all of the files in the Resource List and "Extract" and save them.
4. Reload the neighborhood and open the real Sim you want to resurrect.
5. Go to the Other tab. Under Misc where it says Unlinked: 0x0001. Change the 1 at the end to a 0.
6. Click "Commit" and save.
7. Open the Sim's Character File.
8. Remove 7 files from the replica's extracted data folder: Catalog Description, Directory of Compressed files, jpgtgapng image, Object Data, Object Functions, Version Information, and package.
9. "Add" the rest of the replica's extracted data
10. Select Object Data and select the file there.
11. In the Plugin View window change the Obj.Type to Person.
12. Click "Commit" and save.

(This was quoted from the Sims Wiki)