I’ll limit myself to things that aren’t SE changes or could be done with editing existing material.

TPM: Obi-Wan heads out into Tatooine while Qui-Gon remains on the ship.
AOTC: Owen and Anakin have some sort of spat.
ROTS: Palpatine continues his gradual morph into his ROTJ appearance, not suddenly changing.
ANH: Alter R2’s red/blue light to match other movies.
ESB: Can’t think of anything.
ROTJ: The Emperor gives Luke more tempting reasons to join him.
TFA: Starkiller doesn’t exist.
TLJ: No Rose, because Finn’s role is to work with Poe while remaining on the ship.
TROS: Carrie Fischer was alive to film for it.