"Bottom line is adapt or die"

Yes. If the music hadn't been adapted it might well have died by now - but it didn't, so we'll never know.

The only thing to remember is that folk/trad/source/ancient/anon song is more than just music and words. It's folklore, and history, and identity, and politics and, and and.

Just leave the door open when you raid the larder ok?

It's simple. Say where you found it, and use words that no-one will misunderstand.