Note of caution.
In the case of an increasing OAT like this, generally the original calculation should be OK so long as OAT<TFlex.
But it is not always guaranteed because of the constraints used in the calculation.
In the case of a decreasing OAT there are too many other variables to say it's ok. For example Max TFlex reduces with OAT, Min V1 and Min VR increase with reducing OAT. These must be confirmed before the calculation is declared valid.
So Just using the original calculation so long as OAT< TFlex is not the sort of policy a prudent airman should adopt.