I sang the songs with the accents I heard them sung in. - Rowan. On the Helen Hartness Flanders collected recordings, singers from New England sang songs with Irish and other accents, corresponding to the accents of the singers they learned them from. I.E., It's a natural thing to do when a song is learned aurally.
GUEST, VP - in my dad's WWI Army songbook the title is, "That's the Wrong Way to Tickle Mary."
Some people can't help picking up accents. I'm one of those. I spent 6 weeks with friends in England, came back to the U.S. with one of them, and was asked, "and what part of England are you from?" And in Munich, people asked whether I grew up there. I.e., I was unconsciously speaking German with a Munich accent. And in Naples, people I met said, "We can tell you're Neapolitan." Etc. It just happens.
The hardest thing for me is to sing an English ballad with standard American pronunciation. I prefer American ballads, because I don't have to work so hard to say "get" when my mind is trying to say "git" thanks to my mom's Georgia accent which I still haven't got rid of....