I saw everything balanced as the perfect opportunity to rob or kill anyone. There really isn't a set rule against it as long as your characters RP justifies it. You might not want to constantly gang goodies with evils or anything. Just remember you are toeing the line between getting turned evil if you indiscriminately kill good/neutral anything for any reason.

Iltch also kept the veil as thin as possible so magic was always strong and always killed Villagers at any opportunity and took the Head all the time (being a Twist follower following instructions). As a leader of Nexus you are able to interpret and enforce whatever rules you want within reason. You won't be the most popular leader guy on the block though if you decide to go against the grain of tradition, but that's never really bothered me. Heh.

So, it can depend on the Rhyme and Meter's thoughts, but I have always seen it as you can PK as you wish so long as if the balance shifts, you then shift with it in your targeting.

Now I was never a big PKer so my Nexuns did not fight unless the balance shifted. I tended to explore/wand hunt/level/whatever during the balanced times.