> computer programs are treated as literary works under the Copyright Act

So this applies to published adblockers and things, I guess. You could roll your own, just like you could tear pages out of a book you bought. You could mod a game privately.

If the adblocker-or-whatever is published, it's like publishing a mod to somebody's book. Like a script you point at an ebook that changes it. Is that considered the same as publishing a copy the book with small parts changed? Why?

The article highlights the line in the German copyright act about exclusive rights to "the translation, adaptation, arrangement and other modifications of a computer program". I'm unclear on the scope here. I don't think this applies to people making edits to copyrighted programs in private.