Why not overwrite the claimed bitrate of a fake file with the real one?

[Fake No Funk]

People ask me quite frequently:
Can't you simply overwrite the "bitrate" information of a fake file with the real one?

Well, it's not so easy, because the bitrate of the file is the one it claimes, but unfortunately the content is not.

Maybe this example explains why:
Assumed you have an image with a size of 200x200 pixels. The file information for this image will of course say: "200x200 Pixels"
Then you resize the image to 2,000x2,000 pixels and save it. The image now indeed has a resolution of 2,000x2,000 pixels, and also the file properties will report that. Even the filesize will (depending on the file format) increase significantly.

However, the source of that image was this lousy 200x200 pixels image. Since you can't rebuild hires information that is simply not available in the source material, the effective, "true" size of the image is still 200x200 pixels, even though it claims to be 2,000x2,000 pixels.

You can't tell the image: "Hey, you fake file, you are a lousy 200x200 pixels file" and overwrite the file properties. Because then it would no longer be possible to decode the image properly, since its physical resolution is 2,000x2,000 pixels...

Same for audio files. If the bitrate claims to be 320 kbps but the source was 128 kbps, you can't change the file properties without making the file unreadable...