One more thought, I agree with BJ, that the original words, when they were not intended to insult are usually appropriate - and if they were intended to insult, I doubt I'd have any interest in singing the song anyway.

I sing a song about the heroics of a confederate regiment (the 6th Louisiana, primarily an Irish Regiment) ... and never considered the song offensive in any way, but have seen some negative response to the song (very little - most crowds love it). Some people think it is never correct to think there is anything heroic about the confederate cause, and therefore nothing could be heroic about the confederate soldier. I am sorry that a few find this offensive, and sing it anyway.