a) I think that the language of all songs is malleable. You just have to look at the evolution of Child ballads as they made their way from the British isles to America.

b) We are perhaps being a bit general when it comes to the "English accent". Perhaps we are thinking of Hugh Laurie's Etonian voice as the model here because of the context of the thread, but this might be misleading. But the British Isles has a pretty exciting linguistic diversity. I don't think blues lyrics would necessarily sound so alien among many of our dialects. I'm not a blues expert, but just be provocative - I just looked randomly through some of the lyrics of my favourite, Robert Johnson, and I don't think there are many things there that would sound out of place coming from a Scouse mouth.