Hi hiccup,
Thanks for your reply.
I used to have the cover art embedded in flac files. Since I prefer very high resolution covers, I decided to export them in a separate file, one cover file per album and link them.
By removing covers, size of the flac file is not reduced, so you need to convert the file again, or use metaflac tool, to really free that reserved space inside the flac (padding).
The ultimate goal is to free up the space previously used in each flac file to store the cover art, and be able to identify which files would need to be reconverted again, without having to use MP3Tag. I was thinking in adding that VirtualTag as a column.
Thanks again!