Some changes could be explained through just altering your perspective while watching the ST.

Say in ROTJ:R Boba Fett doesn't end up in the Sarlacc (I have no idea if this is the case it's just an example) and in the ST they make a big thing about Fett being eaten by the Sarlacc, now there you can just say at some point, later than ROTJ:R Fett got himself eaten by a Sarlacc (there must be more than one of the things).

Similarly if Hayden comes back as Anakin Ghostwalker you can watch the film and think at some point Anakin's ghost stopped appearing as the old guy Luke just met and started to look like the young guy he has read a lot about and probably seen holograms of.

It's more difficult if you kill of someone you know or strongly suspect is going to be in the ST.

Leia survived the theatrical OT and the SE and Carrie Fisher is strongly rumored to be returning so it doesn't make sense to kill her off because it's impossible to think your way out of it without a Genesis torpedo.

I hope they throw us lots of clever surprises but some things are going to be easy to spot and dodge.