The folk process can being about improvements but in the case of a carefully crafted modern song, it's unlikely.

For instance, I've heard "Irish" versions (possibly the Fureys?) that replace "The trenches have vanished, long under the plough" with something about "the sun shining brightly from under the clouds" or similar. This makes little sense (how did the sun get under the clouds?) and loses the reference to the lost trenches. It's not a deliberate change, it's a lazy forgetting-and-reworking of the words that has been equally lazily copied by others.

On the other hand, there's one change in the "internet" version quoted above that I think is for the better. The line in verse two: "Forever enshrined behind some glass pane" is replaced by "Enclosed there forever behind a glass pane." I think this is better because the word "enshrined" is already in that verse a few lines above, and it avoids that repetition.

I suppose what I'm saying is that as long as people think about what they're singing, and make deliberate, informed choices, the result is likely to be pretty good. What is not so good is lazy and thoughtless churning out of words that don't make sense, or which lose some of the subtleties of the orignal version.

Marje