An apparatus includes a shaft assembly and an end effector. The shaft assembly includes a first coupling member and a second coupling member. The first coupling member and the second coupling member are configured to flex toward each other from a first position to a second position. The first coupling member and the second coupling member define a pivot axis in the first position. The end effector includes an ultrasonic blade and a clamp arm. The clamp arm is configured to couple or decouple with the shaft assembly when the first coupling member and the second coupling member are in the second position. The clamp arm is configured to pivot toward and away the ultrasonic blade about the pivot axis when the first coupling member and the second coupling member are in the first position.