As has been pointed out, V1 for flex or Assumed Temp is always available, and calculations always take into account VMCA/G for TOGA thrust.
HOWEVER- A Fixed-Derate (TO1 or 2 on some Boeings) only takes into account Max thrust at the derated setting, so using fiew-wall TOGA may exceed the allowable thrust re VMCA/G
One thing I have to consider on my aircraft (777), if changing thrust setting on the roll is to recheck the stab trim setting, as the nose-up pitching moment with the thrust increase wiill require a different setting
Not needed Zlin- the 777 has a speed trim, so the setting is the same regardless of thrust.