Old Fella is right to an extent - it's the same objective for derate vs FLEX thrust.
However the procedures, and accompanying limitations, are separate and distinct. Derate is accomplished in fixed increment(s), and may be applied whenever TOGW vs RW available permit.
FLEX (ATM) is continuously variable up to 25% reduction, but it's prohibited w/ contaminated runway. An engine condition monitoring program is also required with FLEX to assess engine health.
And both procedures have been around over 30 ++ years - long before FADEC and other magic boxes existed.
