Well, I accepted the idea that literature can change how you view the world a loooooooong time ago, so he's just stating the case a little more dramatically and attempting a more rigorous framework than most, I think. If The Invisibles is a living sigil, then so is Das Kapital or Mein Kampf. Or even The Audacity of Hope!
Actually, just reading the letters pages would probably be enough to rearrange pliable minds if you were already sufficiently invested in Morrison's ideas or fiction already.