I'm changing from MP3 to Flac and search for a solution to copy tags from my existing and fully tagged MP3-files to the Flac-versions (copy should be 1:1 including images).
Mp3Tag seems to have a solution for that: forums.mp3tag.de/index.php?showtopic=8704
I think an Opus script could also be made to do it but, since it's a big, one-off task, it probably makes sense to use Mp3Tag which is tailor made for it rather than rig up something in Opus.
Your idea helped. Years ago I found a tool called "Tag.exe" (187 kb) for editing tags - I use it in DO for removing tags, but never thought that it would also offer a copy-tag-command 
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