I'm looking for a utility that will merge data in different tag types. I now use foobar2000 to write gain info to ID3v2. But I have gain info only in APE tags on a small minority of files that Mp3Gain can handle, but foobar2000 cannot. I don't know why that is, but it happens in about 1 of 300 files. I tried to upgrade Mp3tag to a version later than 1.4.6 that will write ID3v2, but haven't found it yet. I would only use it for exceptions since foobar2000 is much faster.
Mp3Tag can merge the two types, but it takes some work. Load the ID3v2, export the tag data you need. Load the APE. Import the tag data. Save. Remove APE tag. All while toggling the Read-APE box in Options. I would like to see a tag merge option in Mp3Tag, but it appears that requests for it have been ignored for many years.
Your action group seems a bit kludgy too. Here's a thread from 2007 that bolsters my contention that the problem has been ignored for years. It's interesting that ohrenkino suggested the same kludge I have been using.
I found a partial solution for the files Mp3Gain can handle, but foobar2000 cannot. It's Mp3GainPRO. It's only value to me is that it completely rewrites the file into something FB2K can handle, but it is audibly louder than the original! When I reapplied the gain in FB2K it went from +56.0 db to -6.40 db. I may eventually get nags to pay for Mp3GainPRO, but I can't see doing that for an exception handler that isn't even consistent with its predecessor! Mp3gain 1.4.6 was used previously.