Originally Posted by HarryT
An ePub file is just a renamed ZIP file, so you can simply rename the ePub to ZIP, open it with any tool that handles ZIP files, edit the OPF file, then put it back into the ZIP again. That's the beauty of ePub - you don't need any special tools.
Well, you do need to zip it up carefully. One of the files must be the first one in the zip file, and uncompressed.
Luckily I've written a nice AppleScript that does that for you