But on an assumed temp T/o with full or derate u need to move up the TL as ur present thrust is way low and the Vmcg is not restricting u.
Actually, no. Performance for ATM is calculated for the OEI case anyway, so there is no need to increase thrust. It would be easy to do so for the full rated ATM case, however for the derate ATM case you do not know where the max thrust for that derate is and you might bust it if you just push the thrust levers forward. Leave them alone, it is all safe if you used correct performance data.