[MGlitch]

I find myself in the same boat, I didn't think I'd like Night Mode, but ended up loving it.

It's tedious, but I'm using Photoshop to invert the cover.jpg that Calibre saves in its library. The tedious bit comes in with getting the images, it doesn't seem PS has a way to open all images within multiple folders without making aliases to those folders. Which might not be an issue except the images are all in calibre library/author/book title.

So while I save myself a few keystrokes by just making an action in PS to invert, save, and close, I still have to open each image.

Once I'm done with all the ebooks I have, I'll use the method David suggested of sending covers to the device. Already tested this with one book and it worked perfectly.

I've thought about getting the images out of those folders in some way, but that adds way more involved work on the backend as I'd then have to match up all the covers with the book.

I figure that if, at some point, I decide to go back to regular I can just have Calibre batch download cover art again and let it replace the inverted images.

ETA- All done now, I was done inverting the books about an hour ago, which means it took me about two hours to invert all my covers, though I wasn't exactly rushing. Not sure how long it took Calibre to upload the images for all the ebooks, I set it to go and walked my dog. When I got home it was finished.