Some episodes “changed dramatically” because of this, he said, and in the case of at least one legacy character from the beginning of Rogue One—as well as “a couple people in we wanted to have in Yavin”—that undisclosed role will be played by a different actor.

I'm guessing "Tivik" aka the guy Andor kills at the start of Rogue One. I'm guessing that character gets a bit more backstory during the final arc of the show.

I'm also guessing the Yavin character is "General Dodonna" aka old man with big white beard. Previously played by Ian McElhinney in Rogue One, which was already a recast. I pick him because he's the only recognizable character on Yavin.

Also I do expect Jimmy Smits to show up as Bail Organa at some point. I expect he'll achieve something "impossible" and he'll comment on how strong/resourceful his family is. We won't see Leia because I think that lessens her impact/surprise arrival in Rogue One, but it will be a clear nod.