I know what you mean by changing tempo (though a song can change from 4/4 time to 3/4 time and still remain at the same tempo. Tempo refers to beats per minute), but what do you mean by changing melody?
In the classic Pop song construct, there is the melody of the verses, a different melodic line in the choruses, and in many older songs (though not all) a third section, called the bridge (in the U.S.A.) or middle-8 (in England), again with its own melody
So any song with both verses (all songs) and choruses (many, but not all) there is a change in melody. Are you asking for songs with two different verse sections, each with its own melody, different from the other?
Interesting question, one I'll have to think about. Not that many, I have a feeling.