Picard manages adding file extensions automatically. By default it keeps file extensions as is.
Sometimes it would be useful to allow changing the file extension with scripting. E.g. if files are saved as .fla instead of .flac. It should be possible to manipulate the file extension in scripts by something like e.g.
See discussion at https://community.metabrainz.org/t/incorrect-extension-value/460939/3