The N word is in more than one spot I think, in The Mikado. Don't know about KoKo's little list. But what I do recall is the Mikado's entry song, about "to make the punishment fit the crime." There is a line "is blacked like a N* with permanent walnut juice." This turned into "is painted with vigour and permanent walnut juice," which prompted Martyn Green, in his Annotated G&S, to venture, "what colour is vigour?"