Originally Posted by slantybard
4. Delete any file with ".css" in that folder or the sub-folders
5. Delete any file that ends with ".xpgt" - it is usually called "template.xpgt" but occasionally comes in different names
The only problem I see in step 4, is that any special formatting for the book, regardless if you want to keep it or not, is then removed from the file never to be seen again unless you have a backup or another copy of the file you download. Sometimes there are elements that enhance the appearance of the book that it would be nice to keep, so it is cleaner to just modify it instead of removing all of it. But as far as xpgt files go, most of the time those are safe to remove, as they are only used by 'Digital Edition' readers anyway.
I personally don't use calibre to modify epub files, as there is very little in the way of fine control. I would instead suggest installing Sigil, and edit the epub files that way.