I accept the simpler David just killed Walter and mimicked him exactly and the cheat of time of what we see on screen and all the tasks that David had to do.
So be it. It’s poorer for it.
However, the potential and idea of David uploading into Walter is more interesting and makes better sense.
In respect of David cutting his hair, I think his intentions although nefarious was partially to identify with and turn Walter as well as using it as a potential advantage should his intentions to get off Planet 4 are confronted.
Before that occurs David spends his time trying to persuade Walter before attempting to kill him
Regarding regeneration etc. of Walter’s model. I think that only went as far as an emergency reboot.
David thought he knew exactly how to disable Walter permanently in one action. That to me was the ‘update’
The film itself doesn’t explicitly highlight or show Walter getting even a minor cut and it healing instantly.
I also question that final pained look back by David after killing Walter etc before running for the ship.
What was that for? Elizabeth Shaw ? All his Work ? Or maybe his own body?
But back on topic, I honestly think there was something intended whether to confuse or reinforce with That Scar that is made so visually prominent.
Thoughts on Re: If David did upload to Walter, why couldn’t he recall the Cabin on the Lake?
David took over physically and could very probably mimic Walter’s voice anyway (Oh yeah, remember how damaged David’s voice box is in that final fight scene? Did he fix that too?)& would have all the knowledge and access of Weyland Yutani to operate as he pleased so that wasn’t inherent to Walter.
In the staple the scar scene when speaking with Daniels, David replies with ‘It’s my duty’ , something he heard Walter say earlier rather than knew from Walter’s memory.
Therefore in upload, Walter’s memories and personality were subjugated or wiped arrogantly as superfluous in David’s view in achieving his wider aims.
Anyway all too deep silly and wishful thinking and I know the preposterous physical switch is what’s presented but I’d like to think the scar was trying to hint at something.
Although he does say a lot, Ridley gave this interview in 2017 and was commentating on AI creating its own language and gave this interesting quote in relation to this idea:
‘"They put two AIs together and they were communing," he said. "It already invented a f**king language!
"And they couldn't decipher what the language was so they had to switch them off. What was said and where's it gone? They could have already implemented something we don't know."https://www.digitalspy.com/movies/a844668/alien-ridley-scott-teases-whats-next-franchise/