Orrrrr . .. what about super exciting subterfuge / espionage quests. Imagine if you will... (probably not possible to program lol)
Quest "Set them up the bomb" NPC Dialog - We have intercepted super secret access codes that will give you temporary region access to <insert town with opposite karma of yours>. Your mission is to take this bomb (random block) and place it within town at (x cord, z cord, random y cord between 40-100 to make sure the location is above ground). Please note all chests in this town are protected by invisible super-ninjas that will instantly kill you should you try and abuse these access codes to steal (instant death by opening a chest). Once the bomb is planted, protect it for 5 minutes to ensure detonation. Reward - 5,000 xp (maybe bonus exp for each person killed by explosion lol?).
This would require that the tnt / region regeneration mod be in effect to work. It should be like any blocks placed or destroyed by you will disappear / regenerate within 2 minutes (except the bomb of course).
Also, to prevent stealing abuse by working with people not on the quest, this would require some pretty significant restrictions on what could be done in town when someone has temporary region access. I would say anyone not a a member of the town should be insta-killed by opening a chest in town when someone has this quest. Could have a warning message when entering region "warning - region currently under bomb assault. Chests are booby trapped. You have been warned"