Right 'mutt',
it's all pre-determined by the settings on the fuel control, with it's determination of the OAT and P/ALTITUDE combinations!
No input allowable from the crew (or maintenance), it's factory set!
DERATE is set by the crew, as part of company policy, to lower the internal temperatures of the engine, and, as a result, reduce the power output, to extend the service life of the engine.
Cheers