Here’s my ideas, only a few of which would be truly important:
Jake Lloyd saying he was repairing or fixing 3PO
3PO’s lines in 2 and 3 about flying
Maybe use it to truly make Padme sound like herself when in her queen persona (too much content in diverse soundscapes to work)
Maybe Obi-Wan addressing R2 in vague ways like “droid”
Anakin being referred to as “General” and stuff like that ala NFBisms’ ROTS project
Battle droids (and surfer dude Neimoidian) in first part of ROTS
Anakin expressing something about his son or kid having his lightsaber
Obi-Wan expressing hope that Anakin still can be saved, to Yoda, Padme, and to Anakin himself
Something to beef up the little conversation between Bail, Yoda, and Obi-Wan. Maybe Bail says something about taking Padme and Leia home with him and his wife, so the scene can be re-extended basically to its original length.
Don’t know where it’d fit, but some tiny nod from Old Ben to R2 that he recognizes him or knows what’s up.
Try getting a different performance for Boba Fett in ESB. I don’t know if cloning Wingreen’s performance would work, might just make him speak slowly rather than getting a vocal gravel like you’d want.
Probably don’t need a voice synthesizer for this, but give the tortured gonk droid a more robotic voice.
Han shouts to Jabba at the pit or Carkoon, calling him a son of a bitch.
Vader saying, “Your mother once thought as you do.” (Might be too humorous, as though Vader in his suit had an argument with his wife and just hit the road one day.)
Unmasked Vader/Anakin made to sound like Hayden.
Snoke could maybe say something at some point to foreshadow the retcon about him being a Palpatine proxy.
Something about the Hosnian system.
Poe calling Hux by name rather than “Hugs.”
Also replace Poe’s “big ass door” with something else that fits his mouth movements. Hate that line.
Give someone in TLJ a proper “bad feeling about this.”
Something from Kylo or Palpatine establishing that he’s a clone or in a clone body.
Something to establish that the Final Order is a modified imperial stockpile, maybe from Poe. Instead of being “the largest fleet the galaxy has ever known.”
Kylo’s “you were right.” And his “become a dyad” line. Or anything else to their effect if the tool gives us more freedom.
3PO’s memory wipe “oh my what is going on because you see I don’t know who you people are” dialogue replacements.
Anything with Leia in TROS.
Luke saying whatever is useful in TROS. I’m sure we’d think of something.
Anything with the Jedi voices to Rey.