It's all pretty straight-forward really. If an operator, due to their own particular set of circumstances, environment etc., wishes to change an operating procedure from that laid down by the manufacturer, they must approach the manufacturer with the proposal.
If the manufacturer assesses that there is no problem with the implementation of the suggested amendment, they issue a
NTO (No Technical Objection)........ Simple
If the manufacturer does not approve, they will say
NO!
I know of one case (because I was the proposer) where the manufacturer changed the AFM for all of that aircraft type after pointing out a deficiency. There are many other such instances.
Regards,
Old Smokey