Firstly, the "Save to disk" is basically an export function. It copies the ebook outside the calibre library structure. It will update the metadata in the ebook if you configure it to.
Calibre will also update the metadata when putting the ebook onto an ereader. That doesn't help you as your ereader isn't compatible with calibre.
To update the ebooks stored in calibre, you need to either do a conversion, or use the "Modify ePub" plugin. If you do a conversion to the same format, you have an option to update the metadata including the cover. If you are doing this for ePubs, the Modify ePub plugin will do it without the need for a full conversion.
|