This addon adjusts the way friendly NPC's react to hostile actions by the player.
In most cases, the personal reaction of an NPC to the player (friendly/neutral/hostile) will slowly recover (by 10% each turn, minimum 1 point) back to it's default value over time. If the player doesn't further aggravate the NPC, it will eventually become neutral/friendly again. (Though it will still probably have the player targeted, depending on its ai settings which are not addressed in this addon.) The exception is if the player kills another friendly NPC within LOS, which will result in the NPC becoming permanently hostile to the player in most cases.
Putting a detrimental status effect on the NPC will create a -25 (negative) reaction to the player (in addition to the penalties from any damage caused).
mod.class.NPC.lua (M:timedEffects, _M:onTakeHit, _M:die)
It can be downloaded at http://te4.org/games/addons/tome/npc-forgiveness