Nothing much for it. I try to sing Scottish and Irish stuff as close to an American accent as possible without doing violence to the song. But it's a bit hard to sing (say) The Muckin' o' Geordie's Byre in American. Well, I think Robert Burns asserted that Broad Scots is a "language" and not a "dilect." So some people are sometimes offended. But no one has ever told me that I sounded phoney -- only that I was phoney. Irishmen sometimes look at me oddly, out of the corner of their eye, and say "very interesting." You cannot please all of the people all of the time.