The vortical spin of an object is a side effect of coherency and velocity. All energy travels with a vortical motion and the more energy moved, the faster the observed rotation. When a bullet is fired from a barrel the barrel does not have to be bored with a vortical groove to set the bullet spinning, it merely needs to be true.

The spinning aids in keeping a true trajectory in an atmosphere by reducing friction and therefore minimizes drift. Where there is no atmosphere, the spinning does not reduce friction and turbulence and does not increase velocity.

Increasing the rotation rate of an asteroid as it orbits the sun would not increase its orbit and slowing it would not decrease it.

Attaching a rocket to an asteroid and adding any energy to its trajectory will increase its velocity and rotation. Attaching a rocket and firing it in a manner not in alignment with its trajectory will reduce its speed and subsequent rotation until such time as the rocket and trajectory are again in alignment - at which point the rocket would act to increase its velocity and rotation again.

Rotation alone does nothing in this instance.