I have never tried to make a Henry rimfire trigger adjustable. Being Henry's rimfires do not have a rebounding hammer improving the trigger pull is straightforward job of polishing the seer and hammer notch. I am not sure why you would want to change the trigger pull once it is to your liking but when mine gets back from Henry I will have to do some work on the trigger being they replaced the trigger and seer. I like tinkering with things so maybe I see if I have any ideas on it.
