How Do I only search for Album Art and only udpate album art?
Album Art
Ok at the moment the album art is done on the asin (amazon id) although this may change. So you could the following:
Edit the MusicBrainz Settings AutoFormat tab to only populate the Amazon Id,
(this is the bottom option)
Run Tag from MusicBrainz
Run Get Artwork from Internet
Delete the Amazon Id field from the UserDefinedText fields if you really want to
Save your files