Tony,

Even Slim Dusty sings with an American accent - he always has done - he might deny it but you listen to "The Pub With No Beer"!
I would not dare to put on another accent (Scots, Irish) unless it was in fun and I was inviting people to laugh at me as well as with me. But I will leave dialect words in a song, as changing them can also change the song, and just sing in my own gorgeous Aussie accent.

Cheers
JennieG