You can batch submit barcodes to the Musicbrainz via the webservice, this provides an easy way to get this information into Musicbrainz for a set of releases. Unlike other webservice submissions submissions are not autoedits if the release has an existing barcode so can clog up the edit queue. But if the barcode is the same same as the existing one then it should be disregarded as there is no real edit.

FYI http://forums.musicbrainz.org/viewtopic.php?id=3214