I don’t think there’s a way or at least I don’t know how to do it.
I now that if I add a folder.jpg to the folder it will get that image as the image for the folder. I have one for my main folder, movies & tv shows. Every time I refresh metadata it loads fine except the library icon. I want this because I share my folder and it would be nice to have all of them working automatically. Not having to long-press in each Apple TV to change library icon.
I already tried:
Library.jpg
Library_icon.jpg
Also, Library icon seems to be bigger than the rests. I used the same icon for a folder & library but the one in library zoom out vs the other that zoom in the image. It’s not a big difference but you can notice it.
Btw, since icon sizes are different between iOS/TVOS it can detect which folder.jpg load per device? Some of them looks too small in my iPhone/iPad.