Oscar Isaac has a very distinct voice and switching between a voice actor and his real dialogue would likely be somewhat jarring. The alternative is to redub his entire scene which is also very likely to be noticeable. Also the lines added are not game changers. You could accomplish almost the same thing with just cuts.
Okay, here’s what it would look like if I used cuts instead of voice acting:
Poe: “We retrieved the intel from the First Order spy, and it confirms the worst. The largest fleet the galaxy has ever known: the Final Order. Hiding in the unknown regions, on a world called Exogol.”
C-3PO: “Exogol does not appear on any star chart, but legend describes it as the hidden world of the Sith.”
Maz: “We must find Exogol.”
Rey: “General, may I speak with you for a moment?”
I’m worried it might be too short, but it could potentially work, especially with a changed opening crawl.