One possible reason to change the words to a song (particularly if it's a traditional one) is that it's in a dialect you can't really do justice to.

For example, a song I *adore* singing (I think its title is "Bonnie Young Man", but I'm not sure) is in Scottish dialect. The first couple of verses go like this:

There cam a young man to ma daddy's door, ma daddy's door, ma daddy's door,
There cam a young man to ma daddy's door, cam seekin' me to woo

Chorus

I took him in, into the bring. I gave him bread and ale to drink
But ne'er a broon eye would he blink, until his wain was foo

For years (and years... and *decades* actually), I wrestled with whether to sing it:

1) with a Scottish accent -- given that even *if* I do a reasonable job of it, there's the issue of whether or not it's inappropriate and/or presumptuous and/or affected for me to "fake" an accent that's not even part of my own background/family heritage (which in itself is (and -- I am sure -- has been) a subject for an entirely different thread or 80)

2) without a Scottish accent, in which case I think it sounds pretty strange & just doesn't work

3) not to sing it at all -- or only when no-one else is around

4) go ahead & sing it with a Scottish accent -- but introducing it with a sort of "apology"

Over the past 2-3(ish) decades, I have opted for #s 1, 3 &4... but -- after a recent discussion with others who particularly appreciate traditional songs/singing, it was suggested I sing it "in my own voice", changing words here & there as necessary to make the song work; not necessarily changing the word "wain", for example -- you can explain to an audience that it means stomach if you need to -- but changing it perhaps to something like this:

There came a young man to my father's door, my father's door, my father's door,
There came a young man to my father's door, came seekin' me to woo

Chorus

I took him in, into the bring. I gave him bread and ale to drink
But never a brown eye would he blink, until his wain was full

Have only just started working on it, but think this might be the best option...

Cheers,

YY