That's precisely what's happened wiith songs throughout history. They get changed, intentionally or through lapses of memory, and that's why we hacpve variants and families of songs.

"Trad is different" No it isn't. Someone made up the songs we think of as traditional, often a lot more recently than people realise.

Ownership and property is one thing, but they've got nothing to do with the ethics of the thing. Unless makng mney comes into it, in which case there's an obligatin to pay up. Manners comes in if you know the person involved, not otherwise, in how I see it.

I'm very much of the opinion of Sydney Carter here, and not his executors. He believed songs should not be seen as property so far as changing tgem was involved, and welcomed tge idea his sngs might gve birth that variants.