The best part about the change is we would only have to modify Kylo’s masked lines to Rey and one Palpatine line he says when his mouth isn’t visible: “It is your birthright to rule… here.” It would be changed to “You were engineered to rule… here.”
Here is a draft of the reveal and force-Bond duel:
“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. Darkness is in your blood. Rey…”
“You’re lying.”
“You were right…your parents were no one. Vulnerable to the allure of a Sith cult.”
“Don’t!”
“Your barren mother… she took a liking to their prize jewel…”
“I don’t want this!”
“…you were adopted from the hoard of the Sith.”
“No!”
“But their actions had awakened a sleeping dragon…”
(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 paid for your protection…in more than one way.”
“Stop talking.”
“Rey…I learned what happened to them.”
(Cutaway to heroes capture)
“Your parents sought sanctuary on Jakku, chasing rumors of a congregation dedicated to Skywalker’s Jedi. But they couldn’t escape the sweeping shadow of the Sith.”
(Rey sees her parents get killed.)
“So that’s where you are.”
“You know why the Emperor’s always wanted you dead. I’ll come tell you.”
…
“Why did the Emperor come for me? Why did he want to kill a child? Tell me.”
“Because his spirit chose another vessel, rendering the others created by his followers as threats to his rule. Rey, you… are his clone.”
“You were created to sit upon the throne of the Sith, a vessel for the Emperor’s conjured spirit. But what he couldn’t foresee was our connection in the Force. We can kill him, Rey, destroy the Sith…and bring a new order to the galaxy.”
(Removes his helmet)
“You know what you need to do. You know.”
“I know.”