Christensen’s ghost is staying and that is non-negotiable. The only thing I’d be open to is replacing those particular shots with a different version without the creepy staring, but I don’t care enough to make such a thing myself, so unless someone else makes it, it’s not happening. Old man Shaw never existed in-universe so having him show up is just absurd. For him to be played by Shaw he’d have to still be scarred and bald at the very least.
As for HAL, that must be where I got the idea from. I’ll write that down for now.