Other than the actual VFX challenge of changing the hilt, is there any reason why Anakin’s saber couldn’t be replaced by Luke’s green saber for the entire ST? This TLJ concept art shows it. It would clear up a few things in TLJ: we’d clearly see Luke reject HIS saber, rather than just rejecting the saber his Dad killed all those kids with (which would be understandable even if he wasn’t so disillusioned!); and it’d make his attempt to force project himself to Kylo as Kylo would remember him be more accurate (Kylo would never have seen him with the blue saber before). There’s no explanation for how the blue saber wound up in Maz’s basement anyway so that doesn’t matter. It’d make the two sabers which defeat Palpatine in TROS be the same two we see in the flashback, more cleanly representing Luke and Leia. Ditto at the end - the lightsabers directly correspond to the two ghosts we see, and there’s no room for “I don’t like sand” jokes to undermine the moment.
Plus green is my favourite saber colour.
You’d have to cut Maz’s line where she says the saber belonged to Luke and his father before him. It would also feel weird to have Kylo say that the lightsaber belongs to him, since it would be Luke’s personal saber and not the one passed down from Anakin (whom Kylo worships).
I wouldn’t have really had an issue with the saber being Luke’s green one from the beginning, but as it stands the blue saber is baked into the ST pretty effectively.