If it's rock, then just say "rock" and if necessary, explain that certain elements of the song echo some folk or trad tune.
Isn't that exactly what the description 'Folk/Rock' does Bill D? If, as was the subject of the thread, we are talking traditional words and tune here, then it's still the same 'folk' song.
If the entire feeling & experience of a song has changes so that those who like the earlier version can't stomach it, then you have *something different*
With tongue firmly in cheek here Bill, haven't you just described the 'folk process' ;) But, if that 'something different' introduced that song to an audience that would otherwise never have heard it, should not the response from those who like the earlier version be more along the lines of 'I don't like that musical style, but at least the song is being sung?
Not sure about the 'screaming vocals', never done that myself. I came to folk/rock via acoustic or unaccompanied song, which I still, of course have a great love for, and I've always considered the words to be the most important of the elements that make up a song, and hopefully, when performing my words can be heard, and the songs recognised for what they are.