Most of the changes for this idea could happen with replaced Kylo dialogue during his two conversations on the Star Destroyer, since that is where he talks to Rey about her past. Changes are in bold:
“Rey….wherever you are…You are hard to find.
“You are hard to get rid of.”
“I pushed you in the desert because I needed to see it…I needed you to see it…who you are. I know the rest of your story. Rey…”
“You’re lying.”
“You were right…your parents were no one. Scrap dealers working on a Sith fleet.”
“Don’t!”
“But you were strong in the Force, so they sold you on Exegol.”
“I don’t want this!”
“You repressed their betrayal”
“No!”
“But then…they stole you back.”
(Rey sees the vision of her parents and her abandonment.)
“My Love…be brave.”
“You’ll be safe here…I promise.”
“Come back! Nooo!”
“They rescued you from Palpatine…and paid the price.”
“Stop talking.”
(Cutaway to heroes capture)
“Rey, your parents sold you to the Emperor, to be trained from birth as a Sith. But your parents regretted their decision. They found you, and rescued you. They wanted Luke’s protection…but they never found him.”
(Rey sees her parents get killed, and Vader’s helmet is broken.)
“So that’s where you are. You know why the Emperor’s always wanted you dead. I’ll come tell you.”
…
(In the hangar, the revelations continue)
“Why did the Emperor come for me? Why did he want to kill a child? Tell me.”
“Because you are the heir to the Emperor, adopted by Palpatine and raised in his shadow. And you know his only weakness. I’ve felt it.”
“You were being trained by the Emperor to rule the galaxy. By the time you were six you were learning the secrets of his power. Darkness is your destiny…just as it is mine. Join me, Rey, and we’ll kill him…together.”
(Removes his helmet)
“You know what you need to do. You know.”