There is a work around that allows you to keep the Safari 11 website auto-play preferences while deleting preferences, but it isn't convenient.  In your mac's user library go into the Safari folder.  There are some files with the name PerSitePreferences.db.  If you right-click on each of these files and click "Get Info" in the pop-up menu you will get the info pop-up menu for that file.  If you check the "Locked" setting those files aren't erased by Cookie 5.6 or Safaris' built-in "Clear History" selection.  Also, any changes that you make to the preferences in Safari while these are locked will not be saved, they will have to be unchecked again.  See attachments.

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