My hearing isn't great so I have probably altered many songs by mishearing. However, one that I have altered deliberately is "Still Got the Fever" by Ian McNabb former leader of the "Icicle Works" and sometime member of the Waterboys.

He has a line in there which goes "I still get excited at the silliest things, I can't keep from smiling when the birdies sing." which I wouldn't class as one of his best. Everyone who knows me is aware that I'm a big Buddy Holly fan so I have altered that line to "I can't keep from smiling when Buddy sings"

It makes me happy and most people who hear me sing the song wouldn't know the original anyway.