You don't have to bump his overall to give him a better potential.
Change him to a Kicker (easiest position to make the potential increase) bump his stats, 80-90 = B 90-99 - A. Save him as a kicker, change him back to RB, he'll go back to his original rating but keep his new potential.
Raising any other stat makes him better than he should be, ruins the point of progression.