Momentum will remain the same until changed by an external force. This applies to both linear and angular momentum
Conservation of Momentum
Regardless of the type of momentum wether angular or linear, once the body has left contact with the bed, momentum will be conserved.
There is nothing the pupil can do to change the flight path or increase or decrease the amount of momentum once they have left the bed
That is why the take off for any skill is considered the coaches primary concern.
Only external forces can cause changes to momentum. That may be a coach handling or supporting a pupil, the trampoline bed or gravity returning you back to earth.
The amount of momentum in the body as it leaves the bed is determined by the amount of effort (push) you put into performing the skill. The harder you push the more momentum you will have. If you push too little you will under rotate, if you push too hard you will over rotate.