If someone rearranges the lyrics of a song with a known author, without the author's permission, the author ought, IMO, to be considered entitled to rearrange the face of the rearranger.

If anyone wants to sing a song I've written, and changes it to suit their tastes or memory or whatver, that's fine by me. It's an indication of a song entering into some kind of oral tradition, and that's what I'd always hope might happen to a song I'd written.

I don't think that just because you've written a song you've got any rights over it once it's growen up and moved away, any more than with a child.