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burnafterreading - I do something similar for some friends & relatives, in essence here's what I what I do
- Add the book they send me (via email) to a scratch library
- Remove low value metadata (tags, rating, comments etc)
- Search for and download the best quality cover
- Modify the book (this is an optional plugin) with these settings, basically it strips out existing dross from the epub.

- Polish the book with these settings, this does a bit more 'tidying up' and adds the downloaded cover and updated metadata to the book.

Aside : some would argue that a Polish after a Modify is redundant, but I prefer to do both - typing 'Alt/M' (my kb short for Modify)and 'p' is easy enough, the software and scratch library live on an SSD so it only takes a few seconds.
- I then take a 'peek' at the book with the viewer to make sure it hasn't 'fallen apart', assuming it hasn't, I have a look at the embedded metadata via the blue 'i' button in the viewer - if anything is wrong I investigate & rectify
- Change Preferences->Save to disk to the relevant template
- Save to Disk (desktop)
- Remove the book from the scratch library
- Send the sanitised epub back as a reply to original email
BR