It depends what you mean by "improvement". Does that mean, "broadening the definition to include some other stuff you like that you heard a girl singing with a guitar at a folk festival"?
A definition defines what it attempts define.An improvement, surely, would be to narrow and make a definition more precise and less open to ambiguity.I wouldn't consider it an improvement to a definition to broaden it hugely from what the people were attempting to define in the process.
If you say " a biggish animal, somewhat horse-shaped, covered in broad black and white stripes in an irregular pattern", well that's a definition of a zebra. You could of course change that definition by adding "or a very tall animal with an irregular pattern of brownish blotches separated by paler lines, with two little horn things. This would clearly change the defintion, by including giraffes within the definition of zebras. Whether you consider this an "improved" definition is an open question.
   I consider the definition of folk music as quoted above a pretty valiant attempt to get to grips with a very fluid mental construct. As mentioned earlier by doc.tom, it is not all that sound on context as opposed to content.But it is a useful definition.We all know there is a difference between a shepherd singing "Searching for Lambs" and a football crowd singing the latest rude chant on the one hand, and the Halle Orchestra or the Spice Girls on the other. We know there is a difference, even though you could come up with things that sit mid way on the spectrum between the two.The 1954 definition is a good bash at saying just what that difference is. Enlarging the definition to include some other stuff you happen to like as well serves no useful purpose that I can see.