Yes it it a workaround.
But:
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As you told it works vor VORBIS COMMENT and ID3V2.
I am writing ID3v2 and ID3v1 for compatibilty-reasons and Id3v1 does not work this way. -
And I used both versions of the double-genre-field in the tag-panel. For new albums I used the predefined list for correct spelling and to look for the already existent genre-tags in a group of file (i.e. an abum or an artist) I used the second field. This gave me the opportunity to equate genre-tags for an album or an artist, if I wanted to do this.
But as it seems every "creative" solution has an end: