Liam's brother - as several others here have noted, and as part of my original comment in this thread, some of the evolution of songs I have been singing for years, while thinking I was singing the song faithful to its original lyrics have changed over time, unintentionally. I know sometimes I have changed a word here or there to fit my phrasing, or the odd change to suit my audiences frame of reference (like placenames in your comment) ... but I must say part of my original comment was driven by some of my more recent work.

I have been fitting some old songs to appropriate melodic and rhythym changes - and some of these changes have required lyric changes to make them fit. Perhaps I was feeling a bit guilty about the changes (though I believe they retain the character and intent of the originals).

I have heard some very distinct versions of old folk songs, and I believe this is the way they evolve - that is with particualr singers making significant modifications, on purpose. For example, I had learned a very different version indeed of the House of the Rising Sun, before the pop version hit the streets (which I am not sure is an improvement, but has become the defacto standard) - likewise for songs like Big Rock Candy Mountain, Wabash Cannonball, Green Grow the Lilacs ... the list goes on and on.

I had evolved my version of Stagolee over the years, thinking I was being true the version I learned as a child from Jerry Silverman book - and when I began to find two or three versions listed here (and elsewhere) with words I had never heard, and with meter that no longer fit my version ... I began to realize just how quickly a song can evolve, even when you are not trying! So in this case an accidental evolution has forced me purposely modify lyrics - if I want to add a verse or two from older versions. This seems to reasonable thing to do, and one which is commonly practiced.

And if a little 'creep' is OK, when accommodating accidental changes, maybe more purposefull changes are OK too. So when I though about mutating Rye Whiskey into a killer, driving finger picked 12 bar blues ... well, I guess I was looking for absolution before I sinned!