MC gives the option to set occult status on a sim. I'm not sure where exactly to find the command, as I haven't played with Supernatural, but I've definitely seen the menu; I also have MC cheats, so that add-on may be necessary.
@igazor has mentioned recently that the MC "play with genetics" option gives you a chance to reroll the outcome for an existing offspring as many times as you want. This is similar to the process you can use to generate a child when you're creating a family, although it apparently doesn't change traits. I don't know if it can affect the occult status of the kid as well.
If these options don't work, you can use sim>basic>baby>reroll genetic seed value on the mother before the baby is born, then temporarily age up in CAS to see how the child turned out. You can quit without saving if you don't get what you want and run the reroll command as many times as you like.
