Sim Modder

Sim Modder is a cheat object which can be accessed by using testingcheatsenabled. It was first introduced in The Sims 2 Nightlife. Simply bring up the cheat box by pressing "CTRL" "SHIFT" and "C". Type boolprop testingcheatsenabled true. While holding down shift, click on one of your Sims, and many options should appear. Click on "Spawn". Then, look through the options until you find "Sim Modder".

Sim Modder appears as a baby standing up. This cheat can:

And many other things. You can make vampires, but on some later games, curing will not work. You need to talk to a Gypsy for the cure.
 * Change the amount of skill points a Sim has
 * Change Sims age
 * Change Sims aspiration, including the hidden Power aspiration.
 * Make/Cure vampires
 * Change relationships with other Sims
 * Increase/Decrease Sims aspiration points
 * Add or remove want slots/locks
 * Make Motives increase, decrease, or be in the middle on anyone on the lot
 * Change Personalities
 * Change Aspirations
 * Increase or Decrease Influence
 * Switch Lifetime Aspirations