This sounds made up.
I purchased a song on iTunes a long time ago, during the time that an Apple ID was required to unlock access to the file. I lost access to the associated email address and Apple ID password. I don’t want to steal a song that I morally own. How do I unlock the file without the Apple ID password?
You can’t steal something you already own. Just download an unencrypted copy. There is nothing morally questionable about that.
I did this recently. I bought an album off iTunes and Apple Music fucked my library up so I had to revert to a backup which happened to be before I backed up that album. That album is no longer available for my region, according to iTunes, and iTunes/Apple support has been unhelpful in completely ignoring all my support tickets to ask how I can download a copy of this album I paid for.
Fuck it. I downloaded the album from less than legal ways. I did pay for the album, after all.
For what its worth to OP you might want to look at what laws apply in your area. Many countries may indeed be okay with you downloading a song you already own (as per transiet punk) BUT be against you breaking copyright protection (decrypting it).
Yeah, I had a de-gooogled android ROM that wouldn’t allow me to verify that I had in fact bought an app. So I just downloaded the unlocked apk and it just works.