perhaps he couldve. With a little more luck and better leadership the Bulgarians couldve been beatean. Its just most of the capable generals at the time were either in revolt or been put out of commision. So the best way for Isaac to be a better emperor is to somehow prevent all those rebbelions that ocured throughout the empire. if the empire is held together then i see no reason why with no other pressing matters at hand the eastern roman armies ould defeat the bulgarians.
Aside from that, many of the problems the romans faced were structural in nature. So I guess you would need Isaac to be a reformer emperor if that is possible. Which I doubt givn he was firmly a civil aristocrat I believe.