Clarke's decision to overhaul his game came after digesting a Christmas letter from sports psychologist Bob Rotella.
The English Open was the 34-year-old's only victory last season and he slipped to 27th in the world from a career-best ninth.
It is the second time Clarke has dropped coach Peter Cowen. He flies out on Thursday to link up again with Harmon before playing in the Buick Invitational in California.
As for the mental side of the game, Clarke said that Rotella's letter made him sit up and take notice. Primarilly, Rotella reminded Clarke to exercise patience on the course.