Hi,
Is it making any sense to set up flaperons on 40 size sport aircraft? If yes how they should work (should I set dual rate, adjust the elevator etc.). Thank you!!!

As in landing flaps or coupled to the elevator for stunting?

For stunting sure. Great fun and super tight loops. Probably great snaps too.

For landing you should know that any more than 30 degrees or so and the adverse yaw will have your model crabbing like crazy unless you use some coordinated rudder with the aileron control.