I don’t take the PT as changing the OT. The only part of the OT that it changes is the moment Vader turns and throws the Emperor down the shaft. Outside of that moment, nothing about the PT (or ST) has changed a thing for me in the OT.

For me the PT is Anakin’s story and it is nearly complete. It would be complete if those droids had not ended up at the Lars homestead. For Vader, the OT is about opening old wounds. Even in the original dialog, Vader is after Luke independent of Palpatine. We don’t have clear motivation except the parent child relationship until we get the PT, but it really doesn’t change anything because the OT is Luke’s hero’s journey. And finding his father is his hero’s reward for his victory. Anakin gets a redemption and balances the force in the process, but his story was really done in ROTS. He was a fallen hero. And a lot of that goes back to 1976 with the 4th draft of the original screenplay where Ben talks about how Vader was his student who turned to evil. Vader was always a fallen Jedi in the OT. The PT just told us the details.