Alternative Melodies

What if you were assigned the task of composing new music for "well-established" [popular] songs, leaving the lyrics intact, but changing the music to make sure it becomes a completely new song, from just hearing it, except for the lyrics? The only thing that should remain the same are the lyrics. I am assigning that task to myself, as an exercise, hopefully, to become a better composer, a better musician, a better singer, and perhaps even a better songwriter.