Would that not be legal, as long as my software doesn't contain pieces of the original book copied verbatim?
Would that not be legal, as long as my software doesn't contain pieces of the original book copied verbatim?
Same thing here, if the modifications were happening on the server side and then sent to your browser that's probably not legal
Publishing it, however, is where copyright law kicks in. Publishing is a specific right that you need to be granted by the rights holders.
I don't see how software running on a client's computer that changes rendering of copywritten work is the same thing as publication. Browsers, video players and Adobe's products all allow users to view and modify copyrighted works on their machines, and that isn't publication at all.
Note too that trademark law can still apply. So your Harry Potter can be in trouble even if the only thing that remains is the name and the universe. (You can do a Harry Potter as the horse in your western novel)
[1] See. e.g., https://grr.com/publications/copyright-myth-ten-percent-rule...