1. Go at least 4 seasons. By season 4, the young guy who played Octavian would have been mature enough to play the Octavian-to-Augustus-Caesar transition.
2. Season 2 should have been the triumvirate (Antony, Octavian, and that third dude I always forget) against Caesar’s assassins (Brutus, Cassius, et al.). Season 2 ends with Brutus’ suicide. Would have been nice to see Pullo totally hunting for Brutus at the end, on Octavian’s orders, ready to slit his throat, and finding Brutus’ dead body, thwarting Pullo and even more so, Octavian.
3. Season 3 opens with that badass scene of Servilia chanting outside Atia’s doorway until Atia comes out, and Servilia killing herself then and there, her sacrifice sealing her curse against Atia. Then Season 3 is Antony vs. Octavian, just gearing up, the thin alliance falling apart thread by thread and Antony being lured away from Atia by Cleopatra, and then finally, Season 3 ends in Antony leaving for Egypt and Octavian throwing down the gauntlet and basically making it known he is going to war against Antony.
4. Season 4: The Antony vs. Octavian war. Actium happens around episode 10 (of 12 episodes).
5. Obvs, in Season 2, Pullo and Vorenus would have been fighting on the same side (when Antony and Octavian were allied). For Seasons 3 and 4, I would have kept the Vorenus-Antony, Pullo-Octavian alliances, but would have made it much more stark, with scenes of Pullo really regretting he was serving on the other side of the war from Vorenus (imagine Actium with Pullo and Vorenus fighting on opposite sides - of course they would have had to encounter one another in the thick of battle but would have let each other go or something).
6. Have Octavian win over Vorenus from Antony late in Season 4, setting up Antony to be weak and vulnerable in Egypt, without his (Antony’s) best protection (Vorenus and whatever Roman centurions were left as Antony’s contingent in Egypt). Thus, Vorenus’ final regret could have been that he abandoned his post, even though it was the right choice in the end to go over to the winning side (Octavian’s).
7. Season 4 ends (series finale) with Octavian making himself Augustus Caesar, and appointing Vorenus and Pullo to the Praetorian Guard, with Vorenus as the Captain of the Guard but Pullo as having personal responsibility for the Emperor’s safety. The triad of characters come full circle from the first episode, when Vorenus and Pullo saved Octavian’s life in Gaul and when they came back, Atia told the soldiers that her boy would need their help in the future. In the final episode, there is a scene where Vorenus and Pullo had to defend Augustus against some attacks by would-be assassins, and even though they kill the assassins, they both know that the assassins were sort of on the side of republican justice, and the Emperor has kind of turned into a vicious, ruthless powermongering dictator. So Rome could have ended on that same sort of tragic/bittersweet note, where Vorenus and Pullo are bound to Augustus for life, but Augustus has completely done away with Vorenus’ beloved Republic and all of those republican ideals. It ends with Rome a mighty empire, and Vorenus and Pullo sharing some of the responsibility for making it that way.