O.K. This would be a nice feature.
At the moment I use a workaround for typical cases, i.e. adding the composer for all my files.
So I have an edited websource-script as duplicate that only grabs the composer, and for being sure to write the content to the right files, I leave some tags-fields as TRACK, ARTIST, TITLE and the length and redirect them to TRACK_TMP, ARTIST_TMP ...
Later I clear these TMP fields in 1 action for some days work.