X-Rays are one thing, electron beams are the other fascinating thing. They are interesting, because they are not only used to observe, but also to modify prototypes and fix bugs.
The modified circuits are not very stable, so it can only be used to verify a fix.
(I learned this 20 years ago, not sure if it still a thing.)
Still used and very useful for test and debug; I worked with Kleindeik Nanotechnik on the process for the Pi 5's little SoC and learned a lot on the way; a little in this blog post but more in the video I linked in it: https://www.jeffgeerling.com/blog/2024/die-shots-and-transis...
der8auer on YouTube also did an even more in depth video on the nanoprobing, at least, and there are a couple places showing the process of etching with electron beam, but not with a very good explanation.
You are correct. You can do mask edits or short runs in some cases beam.
Even more interesting is mask level overlay and CD correction using ultrafast absorption based stress fields. There are some heat technologies out there
The modified circuits are not very stable, so it can only be used to verify a fix.
(I learned this 20 years ago, not sure if it still a thing.)