I sing Paul Simon's own added "concert" verse when I do "The Boxer", but I know it confuses everyone singing along.
Due to cultural factors which have changed over the years, I also change one word in the second-to-last line of the original recorded version (Mason Williams) of "J. Edgar Swoop", which is consistently one of my campfire crowd amusers.
Of course when it comes to altering lyrics I imagine a bunch of us here are like me and my friends - a bit of the "Weird Al" gene becomes dominant when alcohol is imbibed during jam sessions and such
