When it comes to cover art, any time I mess around with Generate Cover after a download to make changes to art, I run the plug-in Modify ePub on the work(s) whose covers I've changed/modified. It works great!
Modify ePub thread:
https://www.mobileread.com/forums/sh...d.php?t=154371
There are checkboxes in Modify ePub for Remove broken image pages, Remove existing cover, and Insert or Replace Cover. I keep the latter option checked by default since 99% of the time when I run this plug-in, it's to add/replace a cover.