I agree with michaelr.

By all means start from your transcription of a particular singer, or a set found in a book but... as you get used to the song, you'll find you start to 'inhabit" it and change a word here and there, alter the rhythm of a phrase here and there etc. etc. Some of this is unconscious, some may be quite deliberate as you find YOUR way of telling the story. Indeed the "problem" with songs like "Arthur McBride" is that people grow so used to one version/set of words that it is difficult to tell the story! Ultimately such songs become "anthems" in the sense that everyone wants to sing along in strict lock-step! Nothing wrong with that - but it's not really what traditional singing is about.

Regards