It's the size of the pie that changes.
1) Consider your airplane taking off, rated thrust, at the max permissable OAT (eg 42C) for the weight, r/w length,
pr alt, gradient, climb perf. etc. and that the accel to V1 is 75%, stop is 25%.
2) Now consider taking off on a std day, but setting Tflex (Tassumed) to 42C. As a first approximation, the accel/stop will still be 75/25%.
But in reality you'll reach V1 sooner because TAS (i.e. inertial speed) will be less at the lower OAT. Thus greater TO margin.
That is, the pie is slightly smaller.
3) Now consider takeoff #2, but using rated thrust. You reach V1 in less time and distance, but the stopping distance is nearly unchanged. So the pie looks like (e.g.) 50% accel, 25% stop, 25% unused. Or, considering only the used portion of the runway (a smaller pie) then it's 67/33%.
Please don't take the numbers literally, but I hope this illustrates the point.