Changing physical damage calculations?

Another question!

Supposing I wanted an effect similar to the Man Eater's doing double damage to human targets, only instead of human, I wanted it to target another special status, such as 0 MP = Death or Undead. Would such a thing be possible to engineer? I'm not quite sure what it is, in the "2x damage against humans" code that actually points to the "human" status, if any.