Erm. I may be displaying my profound ignorance of the system here, but what effect would FPL TAS have on the descent?
Taaarts processing uses FPL TAS & GRIB wind data for calculations in the cruise, and this is why AIP says please tell us if you are doing other than planned. The fix time MAESTRO posits would be largely based on this also I expect (don't know, don't care).
But for climb or descent Taarts uses the performance data files from the bowels of the system plus GRIB rather than anything in the flight plan, and I understood MAESTRO does much the same, from it's own performance data files that know there's a difference to how CSN & QFA fly the same aircraft type.
Whatever the pilot says and we punch in to the flight plan won't change what the machine says. Unless I'm wrong again...