An ultrasonic instrument includes a body, an actuation assembly, a shaft assembly, and an end effector. The actuation assembly includes a mode selection member and an activation member. The shaft assembly extends distally from the body. The shaft assembly includes an acoustic waveguide. The end effector includes an ultrasonic blade. The ultrasonic blade is in acoustic communication with the acoustic waveguide. The end effector is configured to be activated in a first activation mode in response to actuation of the activation member when the mode selection member is in a first position. The end effector is configured to be activated in a second activation mode in response to actuation of the activation member when the mode selection member is in a second position.