He can pass laws under the US system, but surely he is still subject to international law. It would be the same as Milosevich or Saddam passing internal laws - would have no effect on the ability of the UN, or the Hague (have no idea who is responsible) to prosecute for war crimes. Although to date Israel seems to be pretty much immune - does it depend whether you sign up to the Geneva Convention or something?
Actually bush is bribing international governments to make him immune by refusing to give them aid.
http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/11/26/MNGJGA1RUS1.DTL&type=printable