Alex - I believe what you are ?moving to? is common practice.
If you think about it, the tables say you can go at 53T at an ambient of 50deg. Therefore if that is your 'assumed' then it will go and stop at 53T. You are now going to roll at 48T. Thus you will reach V1 (53T) more quickly, ie more runway than required to stop, and more runway left than required to achieve a safe take-off. V2 is higher than need be, so again safe. Yes, a bit like Improved Climb, but you are not actually getting any 'Improvement' in RTOW.
The only cloud on the horizon was once raised in my last company by a friend - who received NO reply!!! Suppose we do the above, but abort at V1(53T), and for whatever reason, brakes, slippery surface etc, overun the runway by, say, 40', and injure some pax and damage the a/c. Would the lawyers have a field day or not when we could have used a lower V1 and stopped on the runway?