I found another nice little gotcha. I decided to give the plugin a try against a DRMed ePub and here is the result.
Code:
calibre, version 0.8.53
ERROR: Modify ePub failed: No ePub files were updated
Modify ePubs
Logfile for book ID 82 (Carved in Bone / Jefferson Bass)
82
Modifying: C:\Users\Jon\AppData\Local\Temp\calibre_0.8.53_tmp_tt05ur\y3j91p_modify_epub\82.epub
Looking for files to remove: [u'iTunesMetadata.plist', u'iTunesArtwork']
Looking for files to remove: [u'META-INF/calibre_bookmarks.txt']
Looking for files to remove: [u'.DS_Store', u'thumbs.db']
Looking for Adobe xpgt files to remove
Found xpgt file to to remove: OPS/page-template.xpgt
Manifest item removed: page-template.xpgt (pt)
Carved in Bone - ERROR: Traceback (most recent call last):
File "calibre_plugins.modify_epub.modify", line 69, in process_book
File "calibre_plugins.modify_epub.modify", line 148, in _process_book
File "calibre_plugins.modify_epub.modify", line 327, in _remove_xpgt_files
File "calibre_plugins.modify_epub.container", line 545, in delete_from_manifest
File "calibre_plugins.modify_epub.container", line 602, in delete_from_toc
AttributeError: 'NoneType' object has no attribute 'xpath'
ePub not changed after 0.16 seconds