Importing custom fields into beets

Most of my tagging has been done using puddletag prior to my becoming aware of beets and I've added custom tags e.g. style, mood, theme, similar_albums etc., so I've no need to utilise musicbrainz as a means of obtaining metadata, rather I want to build a DB and then index and browse by fields e.g. artist to see anomalies and then use beets to make the necessary changes to the DB. Once the DB's correct I'd use beets write to make the changes to the underlying files.

Is there perhaps a way to have beets import custom tags?

No files or tests are named. Start by tracing the import entry point and how tags are stored and indexed in the database. Done means custom tags such as style, mood, theme, and similar_albums can be imported, retained, and used for browsing before beets writes changes back to files.

Written by the indexing model from the issue text.