[derangedhermit]

If I update metadata in an epub in Calibre, is that update immediately applied to the metadata in the epub itself, or is the epub unchanged and the update kept somewhere else until some later time, like "Write to disk' or "Send to Device"?

What about when I download or otherwise change covers? Is the old cover immediately deleted from the epub, or is it retained and the new one marked as an update and stored separately for later? Furthermore, does changing covers actually change what Calibre thinks is the old cover, or is something else going on?

When is a "conversion" (e.g. epub-epub) required to get changes to stick?

Also, the default for writing epubs outside the Calibre library is to have a separate cover page file and a separate ?OPX (some other) file. Epubs don't need these as external files - why is it the default, and what is lost if you set Calibre to just write out the standard epub (zip) file alone?

Last, what specific settings are needed to prevent Calibre from adding its own html (or modifying the existing html) on import, conversion, and export (output)?

I could at least partly answer some of these by exploration, but maybe the answers will be useful to a few other Calibre users.

(I have read what seemed the relevant parts of the help files before asking.)

Thanks,
Lee