Hi David,
I just read all 10 pages of your thread. I am really impressed with all of your hard work. It is amazing the things people, yourself included, can do with the primitive, but powerful, set of constraints, poses, and expressions in AM.
A couple of items in response to earlier postings:
This is a little known AM feature: The compensated force keyframe.
You can turn on compensate mode before doing a force keyframe. Make sure your Key Mode settings are set to include the bones, properties, or poses which you want reset. Then press Force Key. This "Compensated" keyframe puts the values of the properties back to the values they would have had, if the current action wasn't there. Usually, this is the default model state (unless you are working with multiple actions). All the filtered animated properties should be forced to their previous values. This can be done at a later frame to un-squetch your character.
David, you mentioned that you added a couple bones to allow an offset be created from this constrained value. If you set the constraint for "Before Action=ON", then the constraint is performed before the channels in the actions. This allows direct animation of the constrained bone in the action to be treated like an offset channel for the constraint. The results of the action are after the constraint, and therefore added to the constraints result. This can sometimes be used to reduce the number of bones or the complexity of your rig a tiny bit.
Awesome work!
Bob Croucher