If you're singing a song live it's effectively "your song" for that moment (not literally, but in a sense you are responsible for it) and if you feel more comfortable with a slight change in lyrics then go for it. It depends on the audience. For example, I'd feel less comfortable singing the line "I'm going to a foreign nation to purchase a plantation" (Craigie Hill) to an American audience than a European one.

Folk singers change lyrics all the time. Sometimes for rhythmic/phrasing purposes, other times because they find something unacceptable/controversial in old lyrics that were written at a different time. When Barbara Dymock sings "Let Me in This Ae Nicht" on the album "Hilbert's Hotel," she omits the verse that says "let witless trusting women say..." When Katie Kirk recorded "The Snow it Melts the Soonest," she changed the words to speak from the point of view of a woman. I don't see anything wrong with it. Even with songs whose authors are from modern times. I hear minor variations in the lyric of Owen Hand's "My Donal," for instance, depending on who's singing it. All good.