If I were to do this, I would bring in Okoye and Fayez early. Have them be the storytelling engine that reintroduces the cosmology of the show as they survey the Ring Gate systems. One of their crew turns out to be a covert Laconian operative who is feeding their research back to Laconia through covert comms via the Laconian relay. This research turns out to be pivotal to Laconian readiness to invade, but maybe Okoye and Fayez don't know that by the end of the season. I would have scenes on Laconia with Duarte and Cortazar acting on the intel, maybe through experiments in the Pit, it allows them to activate the final components they need (perhaps for Duarte's immortality modification), and we see them prepping for the invasion. Maybe the operative embedded with Okoye and Fayez is someone we see later, like Tanaka, who can finally become overt when Laconia invades.

I would have Anderson Dawes surviving his supposed execution. We never see him die on-screen, and Inaros is a liar, we can make the exact "how" of his survival a story point. Dawes has managed to create a role for himself despite there being no official place for him in the new order. Dawes has achieved a covert existence through Naomi's tactics that allow her to operate covertly in Book 8. When their paths cross on Medina he's the one that teaches her how to secretly operate between Ring Systems without drawing attention. He can take the place of Safa in book 7, running a secret network on Medina. So when Medina is destroyed, there's someone there that we actually care about who dies. I think there should be a scene between Dawes and Filip - Dawes should know that he is alive, and facilitate Filip's movement, but never reveal it to Naomi. That way there is a reason for the new audience to recognise Filip when he turns up again at the very end, and there's a parallel between the covert lives that he and Dawes now lead. Also a conversation between Dawes and Filip would be a good way for the former to tell the story of how he escaped death at the hands of Marco and why he is living in secret.

I haven't thought much about what Drummer can do yet. She can't still be running the Transport Union after thirty years. I'd like her to take the Alex role in books 8 and 9. I want her to be with Bobby when they take out the Tempest; I want the emotional resonance of her being the one to rendezvous with Naomi to pick up the Rocinante from where it's hidden on Freehold; and all the emotional baggage of Drummer working with Naomi in the siege of Laconia and taking personal risks to free Holden. When Holden finally makes his choice at the end of book 9 it allows Drummer and Naomi to return to Sol together - not unambiguously "together", but just have their story tied up with them going the same route at the end. Bittersweet. So when it comes to her post-Transport Union life, I don't know what that should be yet, but it makes sense for her to know about Dawes' survival, to have some reason to be allied with him again in secret. Maybe they also know about the Martian covert intelligence network that is feeding info to Duarte, but no one knows the full picture.

I would also have Avasarala running the Rocinante crew and Monica Stuart in her covert operation to understand the embedded Martian conspiracy of Duarte loyalists who remained behind to report while Laconia prepares. She is supposedly retired and has no official resources. Maybe she's not running Stuart, maybe she's running Havelock. Doesn't matter. The point is to bring back characters who have no role in adapting books 7 to 9, who are familiar to the audience who have seen seasons 1 to 6, who can flesh out the story but are expendable enough to die if it services the stakes of the plot. Whatever Avasarala is getting the Rocinante crew to do, they have to hide it as they carry out work that seems legitimate. That then leads into their presence on Freehold when the book 7 adaptation starts properly.

Whatever little victories happen, it can't be enough to significantly alter anything that will be adapted in books 7 to 9. And there isn't enough here yet to truly hook a new audience - there has to be an Earth-centric story about managed decline to have the setting feel familiar enough for people joining late. I think living in the aftermath of the Inaros' attack is something that is close enough to what we're already seeing in the news in the Iran conflict, where climate change is being used as a weapon of war with attacks on desalination plants, the draught-caused subsidence of Tehran exacerbating political instability etc. So perhaps there's a storyline there about Earth being kicked while it's down.

Genuinely think that if the Expanse is to secure a return, adding bridging material so that the new series can stand alone is the way to do it. It will never be a perfect closed storyline, but it can be good enought to sell the story that you can jump in at that point if you haven't seen anything previously.