Nigel, there was once an old joke in England about a confused sailor who didn't know his Madras from his Elba.

And to the subject; I'd prefer a whole new lyric, a parody, rather than just a verse or two in a Shanty, unless you are one of that rare breed, a working Shantyman. Just my opinion.

However, I have been guilty, as in..
"The Duke of Edinborough gets his finger out...earlie in the morning."
Sorry, Sir and Ma'am.