'the other way' ... as suggested ... would be only in desperation as much has changed when it comes to backups. 'Editing' would require editing xml files and the related directories ... as in the case of files.xml and the files directory. The files.xml and directory is built like moodledata/filedir/. While one could delete files.xml and files directory, that would delete *all files* for all users - including teacher. Plus an .mbz file is truly now a gzip and rebuilding the .mbz file needs to be done so that moodle_ backup.xml file is at the root of the archive or it will not restore.
*Best* option ... reset the course - IMHO!
+1 to Rick's suggestion.
'spirit of sharing', Ken