The Mephisto Waltz (1971)

The Mephisto Waltz (1971) Alan Alda plays a classical piano player on the rise who befriends a famous player himself who's at death's door. Unknown to Alda, the guy is a satanist, who arranges to have their souls switch places at his death, so that he can be young again and continue to play piano (thus needing a skilled piano player like Alda to switch bodies with).