hue is right editting someone elses code is a pain in the butt expecially if it doesnt have proper comments then you basically read through hundreds of lines of code tracing it to see what command or action is located where so you can edit it properly.
however editing,while a pain, is the most effective way of coding these npcs(at least for a PS) because things like "disappearing acts" and npc "sexism" (
) are less likely to happen because even if you dont know how to do it someone has already coded it for you.
might i suggest a coder that can speciallize in editing the npcs.