see the release note for version 2.84: Mp3tag v2.84 released
2 web source scripts are included that download only a cover.
But: there is no way to "prefer" certain types of albums, the search usually heavily relies on the data pair of artist and album.
If you do not want to overwrite files that already have covers, then you can filter for the files that you want to treat:
%_covers% MISSING