[BetterRed]

So, uncheck Save to disk->Update metadata in saved copies option - you only need do this once.

Then, 'clean' the library ePub with Modify ePub by checking the Remove non dc: metadata elements

Now do a save.

If you want to do it in a single click, hack the Modify plugin to do the save after stripping the non-dc metadata - or write an OS level automation script.

FYI: In IDPF speak a 'non-dc (Dublin Core) element' is a 'custom column' in calibre speak.