For CFM56 FRT=32C. I might be wrong, does not matter what the temperature (OAT) input to the FMC. Until FRT (32C) N1 increases and reach limit N1 at FRT, if the OAT continue increases, engine power start decreases, but N1=limit N1. What is the assume temperature? This is temperature when actual TOW= max TOW and does not matter what OAT is. What is the derate TO thrust? This is 5 or 15 percent of Full TO thrust reduction (not of N1).