I think if anybody were to know if Palpatine were lying, it would be Luke’s ghost. I think the fact that he confirms Leia sensed Palpatine’s darkness about her would be enough for the majority of people to buy into the idea. Unfortunately there’s no real way to make this a matter of interpretation without it harming the overall narrative. Finn can definitely still be the one to sell the idea that you can pick your own heritage, though.

Speaking of Finn, I went back and looked at that scene he has with D-O. Unfortunately, he says the entirety of that line on-screen. I’m not sure modifying the beginning of it would be possible, so the Jannah/Lando stuff couldn’t slot in nicely. Currently, all the scene tells us is that Ochi was supposed to bring Rey to Palpatine after finding her since we removed “He wanted her alive”. Now, perhaps he just wanted to be the one to Force-drain her of her life essence to alleviate his failing clone body, that’s definitely possible. Perhaps we could hint at his Force-draining powers a bit earlier so the dyad doesn’t have to be involved by name, and also clear up any misinterpretation that he wanted her alive at that time.

“To bring the little girl that he was supposed to bring from Jakku, to the Emperor. For absorbing her life-Force.” (cue Poe’s sigh of horror).

Then, the audience is expecting Rey to just be drained when she shows up. To instead be confronted by Palpatine being all cheery and goading her into killing him shatters those expectations completely. His priority is to possess her, but when that doesn’t work he resorts to draining the two of them.