I'll throw in my two cents. If it sounds like an affectation, it probably is. But we can sing in an idiom without having grown up in it. How convincing it is depends on who, how and in what context the song is being presented. I wouldn't try to sing a Scottish song with all of the pronunciations entailed but if I were singing Loch Lomond, what's wrong with "bonnie braes"? Grammar is for the printed page IMHO. However, there are songs that misuse words. "Waltzing Mathilda" comes to mind. (It's not in three-quarter time.) I think you can get away with almost anything if you really know what you're singing about. I think you make a horrific mistake trying to come across as something you are not, however. You don't have to wear overhauls to sing a farmer's song.

Frank Hamilton