My experience has always supported the belief that in the presence of full responsibility, offense does not occur. So I am leery of bending too far in the direction of avoiding offense, because I believe it only occurs between two willing participants. This is especially true in the matter of historical records, which these songs are.
All that said, there has been a convention since Elizabethan times of substituting asterisks or dashes for words below the salt, including religious epithets and anatomical descriptions. I don't think we need to redact instances of the word "mammy" or strike "dese" and "dose" or dialectical peculiarities, but pejorative terms are perfectly understandable without being spelled out and it emphasizes the perspective of understanding that you want to promote.