Airlines and aircraft have an ‘Aircraft Flight Manual’ that is a legal operations document. They include exceptions to the rules based on equipment problems and explicit circumstances; those AFM exceptions are part of the rules. There is generally no [legal] latitude for crews to make judgement calls that are not allowed in the respective AFM.
The issue about seat backs and tray tables is to enable the most efficient possible evacuation if needed. I once witnessed a gent who lost his business class seat because he was caught in traffic during the Queen’s visit. He was offered a broken seat that would not recline or another flight. The plane was sold out. He elected to fly in the broken upright seat. I also witnessed a flight where a seat would not lock into the full (or close to full) upright position and it was taped off and could not be used.
Any variance allowed in the latter case would have been in the AFM, not the flight crew’s discretion.
