This comes under the "I don't understand python but I know what the tkinter screen would do" category! BTW, If something like this already exists, can you point me to it?

1. You load in a BVH file. As so often happens, the shoulders are all out of whack.

2. Mark one frame of this as a "neutral pose".

The script then pretends that "neutral pose" is the zero-figure pose made by the joint editor.

3. Using the parameter dials, adjust the shoulders so they look right.

4. Mark that frame as an "adapted pose".

The script pretends that the adjustments you made were to the zero-figure pose. You can now save the adapted pose to the pose library.

5. The script then runs through the whole BVH, applying the same adjustments to each frame.

The difference between doing this and using the animation graph is that you have a saveable pose representing the adjustments. Say you download a large set of BVH's from a website. Provided that all the BVH's were made for the same rigging, you could correct just one frame of the whole set, and then apply the adapted pose to all of them.