Some of the old folk songs don't make good sense, lyrically or musically from a songwriters point of view. It's perfectly alright for someone to "clean up" an old folk song and change the music around, as i do sometimes. Just don't claim it for your own cause you didn't really write it, just changed something that was already there. Doc Watson did it a lot, never heard anyone complaining about him doing it. Long as someone uses the "arranged and adapted by........" prefix it's fine by me and you can copywright your "arrangement" if it's not like anyone else's. I personally don't as i feel it's in really bad taste to do so. A traditional song should belong to everyone. If anyone wants to play my particular version of an old song, go for it.