How do I use a vampire sim as a "template" to create a human sim?

Thanks! Actually, just after I finished writing this post, I thought about the twin thing again. So now I used my humanized vampire saved in the library and created her a twin. She looks closely enough my original vampire, I can't really tell the difference. So, she's a human, and when I tried, she was able to eat human food. Now I'll only delete the original from the household, and then cheat her into all the skills my original had.

Thanks everyone, I think my problem may be solved :)