Off the top of my head:
The revised shot of our heroes zooming towards mos eisley, where they added those scurrier rat things in '97, was further revised in 2004 with a cgi landspeeder.
The infamous Han/Greedo shot was further tweaked in both '04 and 2011 IIRC.
The cgi model of Jabba used for '97 was redone in 2004.
In Empire they did indeed reverse a change from '97 where you hear Luke screaming as he falls. This might be the only Empire change unique to '97 unless there’s other obvious things I’m forgetting.
As for RotJ, in 2004 they added Naboo to the galactic celebration montage and also added the senate building and jedi temple to the Coruscant background.