First off, then if law NPCs can't see who you are, then neither should PCs when you gank them and they try to report you but can't. Sooooooo.....
1) c poly <thing> <adj>
2) Go to city
3) c pet <target>
4) couldn't be reported
Or
1) c poly <thing> <adj>
2) go to city
3) c charm <target>
4) order all remove all; order all drop all; get all; c tele <target>
5) couldn't be report
Or
1) c poly <thing> <adj>
2) go to city, preferably an Inn
3) wear demise; brand
4) go through corpses taking what you like
5) couldn't be reported
Or, for the necros out there...
1) get scrolls of poly
2) get an army of undead
3) recite <thing> <adj>
4) kill city
5) couldn't be reported
Or
............. The list goes on...
This would mean you a) have to rewrite the whole law system, and b) it would be abused as all holy hell.
to your poopy idea. And yes I am a GM sorc who would abuse the holy hell out of it.