Guest: I happen to sing one of this songwriter's songs (not recorded) and I am sure that some of the words have changed since I started singing it. The meaning of the song - as far as my understanding of this song goes - remains unchanged; its just that some words scan easier or lend themselves more to singing for me.

I think that's fine as long as it's changing of unimportant words for a specific reason such as easier scanning, but when words are changed through simple ignorance or mis-hearing, I'd diagree. Three that immediately come to mind are:

Ewan MacColl's "Joy of Living" where his description of a string of hills and mountains in the UK is often rendered "cool big Scafell" (implying one large chilly hill) rather than correctly as "Cul Beag, Scafell" naming 2 mountains, one in Scotland and one in England. This was even propagated in Mudcat until I corrected it a few years ago.

Donovan's "Catch The Wind" where the 3rd verse start is almost invariably sung as "When rain has hung the leaves with tears
I want you near to kill my fear" though the original lyrics are " When rain has hung the leaves with tears I want you near to quell my fear" which to me is a much more appropriate word. I sing "quell" when I do the song, but in the last 10 years I can't think of once when I've heard anyone else sing anything but "kill".

And another MacColl song, "Dirty Old Town", where almost everyone sings "by the gasworks wall" instead of "by the gasworks croft" which to me takes away from the "crafting" of the song as "by the factory wall" comes so soon after "gasworks" that it sounds plain clumsy to use "wall" twice, and does a disservice to the songwriter, IMO.