This is a good note!

Rogue One is something I want to revisit after this last season of Andor comes out, especially if they nail the landing. I hadn’t really thought about Rogue One much since voice AI and vocal isolation software has become more available, so it will be cool to look back at this film with these new tools and see what can be done. Anyway, it might be worth waiting to update this edit after Andor is complete in case there are other issues that need to be addressed.

Looking back at the scene you mentioned, I think you could trim around that line without it being super noticeable, and Chirrut’s line about carrying his prison wherever he goes can work just as a continuation of his thought.
Honestly, his mouth barely moves when Cassian says, “This is a first for me”, so I wonder if you could just mute the line and it not be super noticeable? Or it could just look like he is saying something under his breath. You could potentially use VFX to make his mouth not move though.

Alternatively, you could alter the line so he actually says, “This isn’t the first for me.” You could probably frankenbyte the line with existing dialogue or use voice AI to replace it.