I beg to differ on the "AFM Procedures are legal requirements".
The only section of the flight manual (and the FCOM or other documents based on the AFM) you must follow is the limitations section. It says so in the beginning of the Limitations section, and in the Type Certificate Data Sheet and Airworthiness Certificate.
The normal, abnormal and emergency procedures have no such wording at the beginning of their sections. (Beech manuals notwithstanding - they claim everything is mandatory...). Ergo, it is not mandatory to follow them.
The rub comes in company approved procedures manuals, which are required to be followed by the operating rules. If it's in the approved operations manual, then the company can insist that this is the way to do things. That's different than the airworthiness or engineering certification requirements.
But there is no requirement in the original approved flight manual (the one that says FAA approved on the bottom of the page) to follow only the normal or emergency procedures as written in the manual.
You should have a pretty good reason to not follow it, and sometimes people make the changes without having thought them through as well as they should.