It's true, rb fires can still attack people in TC using their guard. But actually PKing depends on whether or not you can pk the person in a single zap which isn't very likely at all unless they're very low level. Also once your guard gets killed and falls down, you'll still be flashing and probably get killed by the town guard yourself. Make sure you can one-hit or you'll only look ridiculous. But oh well, it's a bug, exploit it. There's always some little nooblet running around you can pick off.
Blacknames shouldnt hang out in tc. You can still kill them because they dont flash when u attk them. everything else shouldnt be attked. Also, you can pk high lvls that are afk for exp :P:P it takes a while to kill them, but if their afk, and they are just out of range of a guard, u can attk them:P
Have you thought for even a second what TQ will do to patch it? Hm... think back to old market days when guards were allowed... They will make tc and plain map a non guard map...
Abuse it all you want the inevitable end I have showed you will just come sooner.