Worse, engineers refuse to set 49" because "bloody pilots will ruin the engines
It shouldn't even be an engineer's unilateral decision, if the manufacturer has specified a minimum MAP and RPM under certain conditions then that's what should be set by the engineer (I assume we're talking about setting the density controller). Are such specifications made in maintenance manuals? It certainly appears the AFM does.
It would be interesting to see whether a charge of manslaughter could be supported if it was proven the MCP was deliberately reduced not in accordance with published maintenance procedures (and I admit I don't know what they are). Fair enough if the operator has procedures that limit MAP/RPM in normal ops but to deliberately derate an engine in a PA31 so it can't get max power is criminal. Wouldn't modifications like that require an EO or STC and revisions to the appropriate performance sections of the AFM?
It might be worth defecting the next one you fly horatio and seeing what happens.