Is there a Reload plugin
 

During development of my ebook converter (for which I use Calibre to test and preview), it is very often necessary to reload the document. Currently the only way I can see to do this is to delete the document, and then open it again from the directory it gets created in.

Has anyone developed a plugin that would provide a Reload button that would just read the new .epub file and replace the existing entry in Calibre?

Just drop a fresh copw onto the BOOKS details pane or in the FORMATS area of the metadata editor (this is also how to add additional formats without doing the conversion)