Not quite sure what you are talking about here?
If you are talking about the filename used when you use "Send to Device" or "Save to Disk", then you can set the mask under Preferences to say how you would like the filename to be made up.
If you are talking about the files stored within the Calibre library, then you cannot change their names without Calibre completely losing track of a file and you effectively corrupting Calibre's database. Files inside the library are not meant to be manipulated directly, but only via the Calibre GUI.
If it is something else then perhaps you can clarify what you are asking for?
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