If we’re to retain to same basic plot and story similarities, then the changes ought to be purely cosmetic:
-Kylo’s saber ought to be a different color, to eliminate the “bad guise use red” cliche.
-No visual callbacks, like the binary sunset, the chessboard, the cantina, etc.
-Starkiller base ought to be a decoy, “These rebels will think we’re stupid enough to build yet another Death Shhtar!”. Ideally they could come up with a more clever way to be threating.
-No “landing after coming our of hyperspace”, it’s enough with the recycled OT moments, why insert an unused concept from TPM?
-No storm troopers, the enemy force would look like a Frankenstein’s monster of an army with many different species and uniforms. No ETs, though.
-No C3P0 or R2D2. Seriously, why are they so important to this universe? They’re just droids that happened to be in a few major battles.
-Have the Millenium Falcon heavily modified, after all the version Han had was not the original to begin with.