Surprised no one has mentioned the Yavin changes. They’re small, but seem to imply the biggest changes to the plot/characters.
First of all, it seems like Jyn has never stopped being a rebel for Saw, and in fact that’s how she got in prison. This means that much of her interaction with Saw is different. I think the hologram might’ve been added as well, or changed.
The whole mission is completely different. It isn’t find Galen Erso, it’s figure out how to destroy the Death Star (which presumably would lead them to Galen). Everything involving Cassian’s mission to assassinate Galen was added during reshoots (I think he was supposed to be a Rebel recruiter or something).
The other thing that’s noticeable in the film (though not based on trailer footage or anything), is that anytime you see Donnie Yen with a wig, it’s a reshoot. This occurred to me in his first scene (when he meets Jyn). This also makes clear the assumption that anything involving the Galen Erso assassination plot is from reshoots.
Do you guys remember people saying that the reshoots were done to add additional shots of X-Wing pilots? Is it possible that the original battle was all on the ground, and that all the space stuff was added after the fact?