I reported earlier I switched to tiny audio files as a way of taqging podcasts at the album level (/t/16895/1 It occurred to me several episode-level tags were fairly consistent across podcast albums (e.g., genre, composer, podcasturl).
This Export Config allows me to fill in any blank episode tags using the tiny file tags as the default. It builds an Action group. The steps are as follows: Maintain Master List of Composers (by Album) >> Run Export Config (in my case, against the tiny files) >> Run Action group. Result: Filled composer tags at the episode level.
Name: Action Group Generator-Composer Fill
$filename('C:...\Application Data\Mp3tag\data\actions\Composer Fill.mta',UTF-8)'[#0]'$loop(%album%)
Sure beats manually maintaining an Action group.
Note: The above ACTION does not affect existing entries, only blanks. I use to indicate tags I really want to stay blank. The Regexp works around a persistent problem I've had with Mp3tag (/t/16547/1 of not being able to escape single quotation marks (') in FORMAT statements (e.g., Album = Kera's Think).
FORMAT statements (especially those as complicated as the one above) are SLOW. You might want to use filters to minimize the number of episodes touched by this ACTION group. For example I only use the Composer Fill ACTION group with the filter NOT composer PRESENT.