Could I make changes to a bootable Ubuntu ISO by booting into it, making changes within the OS, and re-exporting the ISO?

Question

Suppose I have a bootable Ubuntu ISO. I would like to make several changes to the image at the OS level. The changes I want to make include changing the default user password, as well as a few other OS settings.

Could I write the ISO image to a removable drive, boot into Ubuntu from this drive, make the changes within the OS, and then create a new bootable ISO (with my changes) from this removable drive?

Suppose that the image I’m starting with already has some packages installed and custom modifications done, so starting fresh from a new Ubuntu ISO isn’t an option.

Would my approach work?

Or is my only option to unpack the ISO with some kind of software like PowerISO, somehow make the changes in the filesystem, and then repack it?

Answer 1

Would my approach work?

Your question is equivalent to asking "Can I modify compiled software"? Yes you can, but you need the right tools and certain mental abilities for reverse engineering.

Your question itself is a strong indication that you won't be able to do so, because the people that are able to do so would never raise that question in a public forum - they simply do it, sorry.

Your intended modification would most likely require rebuilding the ISO file when your modifications go beyond bit-flipping and involve changes of length of the files contained within the ISO.

Furthermore there is another layer to overcome, when dealing with certain files, they may be compressed and you need to uncompress, modify and recompress them before even building the ISO.