It'd be a form of plagiarism, just with different consequences to the most common form.
Copyright Office requires you to disclose AI involvement and disclaim the AI-generated parts. Zarya of the Dawn is the example — applicant filed for the whole graphic novel, got partial registration on the human-written text, refused on the Midjourney images. The reproducibility of the prompt isn't really the test. The test is whether a human made the expressive choices.
LLMs are amazing of course and we use them heavily ourselves - but not for modifying text that is to be posted to HN. Doing so leaves imprints on the language that readers are increasingly becoming allergic to, and we want HN to be a place human conversation.
Not really. Copyright registration is pretty much automatic. The Copyright Office does not check for duplicates. Patent registration involves actual examination for patentability. Issued patents are presumed valid (less so than they used to be), but issued copyrights are not. You have to litigate.
The US does not have "sweat of the brow" copyrights. It's the "spark" that creates the originality, not the work. Which is why you can't copyright a telephone directory (Feist vs. Rural Telephone) or a copy of an uncopyrighted image (Bridgeman vs. Corel) or a scan of a 3D object (Meshwerks vs. Toyota). Or the contents of a database as a collective work. Note that some EU countries do allow database copyright.
Interestingly, a corporation can be an author for copyright purposes. The movie industry pushed for that. We may in time see AI corporate personhood for IP purposes.