Mmmm, we advised you not to do it 
As mentioned by BSA, re-assembling the freewheel with less balls is of course not good, otherwise the manufacturer would have done it to reduce the cost…
These are the negative effects:
-
Accelerated wear with,on the long term, more lateral/angular play in the freewheel which in the worst case could make the belt climb on the flanges of the rear pulley and damage it.
If you are a sporty cyclist and push hard on the pedals, then the bearings will deteriorate more quickly. -
Less smooth running when not pedalling with potentially more drag and more noise.