Yes, for MP3 you can do this with Picard. Have a look at Options > Tags and set the following settings:
Enable “Remove APEv2 tags from MP3 files”
Select ID3v2 version
Disable “Also include ID3v1 tags in files”
For FLAC files there is also the option to remove ID3 tags.
Not sure what kind of validation you have in mind. What exactly do you want to check? Picard will ensure the tags are technically correct. And of course you can also use Picard to update the tags with metadata from MusicBrainz.
No, not quite. This will just remove the primary tag section Picard is writing to before writing it again. So for an MP3 file this would recreate the ID3v2 tag. But it does not touch e.g. additional APEv2 tags in the same file. And if the concern is just to switch between ID3 v2.3 and v2.4 you just need to change the setting.
The fun of language. So “Clear existing tags” means “Clear the tags of the same type I am adding, but leave everything else as it was”. That should be in the documentation really. I always assumed it chopped all tags from the file and started fresh.
I want to ensure that all info in tags other than ID3v2.4 is also contained in the ID3v2.4 tag. Then I want to remove all the other tags, and be left with only the ID3v2.4 tag.
Does Picard list all the tags in a file? I have a file that a Java library told me has both ID3v1.0 & ID3v2.4, but the Picard info dialog only lists ID3v2.4.
Does Picard show differences between info in different tags in a file?
Once I’ve set the preferences to use ID3v2.4, to not use ID3v1.x, and to remove APE tags, what do I click on / run to enact the change on a file? I don’t want to change any of the data in the existing ID3v2.4 tag. Do I just click Save?