I saw that video as well recently. It’s a cool idea, but I don’t think it is feasible for a fan edit.

I think the closest you could get to an arc of Rey falling to the dark side would be to not have Rey go to Luke’s island after she almost kills Kylo. Instead, you could have it to where Rey thinks her fate is sealed, and goes to Palpatine because she thinks she has nowhere else to turn. You would need to cut any shots of Rey flying the X-Wing, and probably most of her dialogue when she encounters Palpatine. Instead, he just tells her that this is where she belongs, and that the power will be hers if she strikes him down and becomes one with him. And just as she is about to, she senses Ben.
You would also have an issue with Leia’s saber, and wonder where it came from. You could have it where she actually got it from Leia earlier in the film, or perhaps the saber is on Exegol. Maybe on Palpatine’s person. And when she passes the Skywalker saber to Ben, she takes that saber. Having Rey kill Palpatine with both a red and blue lightsaber could be cool symbolism if an edit were playing on themes of balance, or a new era of force users.