Personally, I don´t know how to mod, but I had an idea that could be nice.
Use able sentences for Henry like: ´´Yes of course´´ ´´Where is he´´ ´´I will meet you there´´ and such so modders can make quests. That way the new npc will do all the specific talking and Henry just confirms or denies what the npc says.
think you’d run into copywrite and actor use legal problems.