If you sing a cover song and change something about the track (whether it be lyrics, timing, key), your cover has now become a derivative work. Think of it as deriving from another piece of music and, therefore, become something new. You will ALWAYS need permission to do these.
The Evolution Of The Electric Guitar
The first electric guitars were made in the 1930’s in response to a demand from guitarists in bands whose rhythmic stylings could not be heard above the other instruments.
