Understood. I’d like to leave the APE information intact, but to write some information in the ID3 tags so that I’ll be able to tell (from ID3 info) that they’ve been through MP3Gain.
I think the criterion is already there: once the file has got the gain information it has an APE tag.
So you can easily filter for these files with
%_tag% HAS APE
or for those that still have to be treated with
NOT %_tag% HAS Ape
That’s an interesting way of doing it. Thanks for the heads up.