John Deere would say that you can reflash, smash, or replace the eeeprom if you want. But you can't create a new piece of software based on the old one.
I think you should be able too, because what is the harm, but I don't think the book analogy holds.
You aren't allowed to rewrite a book, even if you keep the copy yourself.
I think you could argue that it is fair use, and maybe it is, but you are creative a derivative work. That is copyright infringement, unless the fair use exception fits.
Hmm. All right, contrary to the law, but wouldn't the damages be zero if you don't distribute? That is, while technically illegal, wouldn't there be no penalty?
I think you should be able too, because what is the harm, but I don't think the book analogy holds.
You aren't allowed to rewrite a book, even if you keep the copy yourself.