The typical one is that Belisarius gets more troops which makes the initial invasion if Italy faster - mainly by avoiding long delays.
I'd personally combine that with a River Pruth Limes and a client alliance relationship with the Gepids to slowly absorb the Carpathian Basin and hold off the Avars. Having that depth of defense in Europe, and an Italy that hasn't been wrecked is good. Not good enough to ensure a reconquest, but provides a solid basis for the future, and changes the circumstances of the Empire. It comes with the advantage of the Gepids having to establish towns, cities, etc, whilst being culturally assimilated by the Romans.
After you have something like that, having Italy be the bulwark and centrepiece of a long-term reconquest effort isn't impossible. The might of a somewhat salvaged Italy and Africa could make inroads into Spain under an heir of Justinian I.
Being stronger at this point, and managing to butterfly away the Caliphate conquering Roman territory, and perhaps even taking a bite of Persia can lead the Romans pretty dominant culturally, and can dominate via soft-power rather than direct control. Essentially taking the role of the HRE/France and the Pope and merging them into one in Constantinople.