Why are the 7/7 bombings depicted at the wrong station in Hereafter?

I'm going to take a swing at this - it was cheaper to CGI one shot than change the tube station signage.

Yes, the exterior is definitely Liverpool Street. This from Google Streets…

^{This, by the way, is the tiny single outdoor entrance. The main station is behind and to the left of this shot, if you're ever trying to compare with photos from the original attack. In the movie, for this establishing shot, the boy is actually walking away from the main entrance towards this one. That only makes sense in movie-land ;)}

We clearly see the boy walk in here at the head of the scene and out again at the end.

Everything else, though, was filmed on the closed 3rd line at Charing Cross. When the Jubilee Line was extended, one old section was no longer required and so was closed. Nothing else was done to it. It still works, trains can go through there. This makes it perfect for the film industry, an entire section of absolutely authentic tube station, complete with escalators and functioning trains - no-one could ever build that convincingly for a set.

It is, however, still decked out in its original Jubilee line decor. I've worked here on occasions where the entirety of the original signage was covered over to make it look like not one, but two different tube stations, one on each of the two platforms they have access to.
This, however, is not cheap to do.

So, my guess is it was just cheaper to CGI one shot of Liverpool Street than change all the signage at Charing Cross. This decision was likely to have been made later in production, as they'd already shot their establishing scenes using the correct station.

Maybe they imagined no-one would notice it was the wrong station, historically.

Here is the Charing Cross location shot from the movie, totally authentic and complete with its original, now defunct Jubilee Line signage…

Extraneous information, not truly important to the answer
For the true London Underground connoisseur, though, this shot confuses me.

Top left you can see a sign quite obviously stuck on, saying Charing Cross. Firstly, you just don't get signs hung from the ceiling like that telling you what station you're in, so that's covering something which in all likelihood says Central Line. Additional Central Line route maps can be seen on the right-hand wall. London tube lines have distinctive colours, Central Line is red.
This shot is, then, almost certainly actually in Liverpool Street itself, not Charing Cross. The Central Line goes though Liverpool Street. It doesn't go through Charing Cross. Additionally, I already know exactly what the top of the escalators looks like at Charing Cross & this is most definitely not it. Where the old station was closed off is right at the top of the escalators, making this shot impossible to do because there's a blank grey wall in the way.

This makes it odd chronologically. Did they film this while they were there to do the establishing shot? If so, they'd already decided to move the plot to Charing Cross. Someone responsible for locations would already know this shot would be impossible at Charing Cross… unless they'd stupidly only discovered it once they got there and had to come back later to get this one.
I guess we'll never know that detail.

There's also a massive break in continuity from this shot to the next, looking down the escalators at what is now actually Charing Cross. None of the people behind him as he approaches are still there when the camera turns round. If we weren't already trainspotting the errors in this scene, no-one would ever have noticed that. It's no biggie, but it does display a certain lack of attention to detail that a production would normally take great pains to not expose. I've been known to be called back weeks later to ensure continuity in a scene like this.