No, the blades rotational speed always remains constant.

Helicopters have to balance aircraft altitude with the main rotor's collective pitch (controlled by the collective handle), the aircraft pitch and roll with the main rotor's cyclic pitch (controlled with the cyclic joystick), and yaw with with tail rotor's pitch (controlled by the foot pedals). Each part of this balancing act effects the other, and all must remain in balance to hover. The rotational speed of both the main and tail rotors remains constant, it is the pitch of the blades that changes rapidly to produce the amount of lift required for the balancing act. if you mounted a camera on the main rotor that spun with the blade, you would see the blade's pitch or angle of attack change rapidly during each rotation.

Spending ammunition does have the effect of reducing aircraft weight and producing recoil force. Both of these forces would have to be countered by the three controls mentioned above, all of which affect the blade's pitch, not the blade's rotational speed.