I think it is something of a false premise that the story could even change substantively in order to accommodate Keanu Reeves when he was cast for the role of Johnny Silverhand.
Tarantino for example did not originally intend for John Travolta to play the part of Vince Vega in Pulp Fiction. Of course, Travolta made the part his own and now it is very difficult to imagine anyone else as Vince but the character existed long beforehand in various screenplay iterations and storyboard concepts. But the screenplay had to have been finalised before casting began and I believe Tarantino's first choice for the role was Michael Madsen (who was not available due to scheduling conflicts). To do otherwise would mean that during casting there isn't sufficient information to give to the actor on who the character is and the what, why and how of what he does within the story. It makes proper casting impossible.
Similarly, the character of Johnny Silverhand and his place within the story had to exist long before casting even began. He is an important character in the source material and what I would consider to be the deuteragonist of Cyberpunk 2077.
There are historical examples of games that underwent significant changes during development, such as Final Fantasy Versus XIII which ultimately became Final Fantasy XV. We don't know how much of the story changed (if at all because it bears striking similarities to Type 0) but what we do know is that it shifted away from the mythos of Fabula Nova Crystalis and there is virtually none of it left in XV at release.
I have heard several people talk about the two as if they were different games and that if there was some way to go back to 2012 and finish Versus XIII, it could somehow be a better game than XV or have a better story. This is absurd and is not how the creative process works. Versus XIII is XV but at an earlier stage in its development. In the initial stages of the creative process where its full of placeholders and vague ideas, things shift and move around until they solidify into something real. Final Fantasy XV is real and its what Square Enix put out into the world. Versus XIII is not.
I don't make games or movies but I do write and record my own music in a hobbyist capacity. You can't write music thinking about what could have been if you continued ambient test 3.1 and took it off on a Deep House tangent instead of what it did and has become. The process doesn't work that way. At some point there is a fork in the road, you make a choice, you rationalise it, you start walking and you don't look back. You just can't be creative if you doubt your own decision making going all the way back to initial concepts.
