That seems to be pretty much the same as in the 737s. We have three fixed thrust settings, all with their own VMCg/a limitation and own performance data (for the 700/300 its 22k, 20k as derate 1, 18k as derate 2) and on top we can use assumed temperature to furter reduce the available thrust.
The catch is that with a fixed derate you have to be careful about your minimum control speeds, simply advancing the thrustlevers to full certified thrust can lead to very unpleasant surprises if you are below the relevant minimum control speed.
A notebook tool calculates what thrust setting, assumed temperature are used and if we used improved climb performance, however we can of course override some settings if we deem that necessary.
Still, it is weird to use 3500m of a 4000m runway until you rotate and our ATCO friends certainly don't like that either.