I don't put on an accent. If it's something that is clearly from the British, Irish, Scottish, African-American, whatever tradition, I at least try to control the twang and my lisp, but I'm lousy at accents and wouldn't insult my audience by trying. I'll tell them that the song is Irish (Scottish, etc.) but don't try to sound like I am.

Conversely, I don't play up the twang for my regular "hillbilly" repertoire and it irritates the heck out of me when people do because it almost invariably sounds fake and patronizing. The Carters didn't like being played up as yokels and Leadbelly preferred to perform in a suit rather than prison stripes. Folk music doesn't have to be undignified. It would be one thing if I really were a coal miner's daughter, but I'm not, and I feel like it would be exploitative of me to "pretend".

I don't make changes unless something can be altered from less to more correct easily and without disrupting the flow of the song. A word or two here and there, but not major restructuring.