Not possible. However, you can destroy the old projectile and make a new one with an adjusted velocity. If you do this, I recommend not doing it too often - perhaps run a simulation of velocity deflection side-by-side with the 'real' projectile, and when the difference between the real and simulated projectiles gets too large, adjust the real projectile (AKA destroy it and make a new one, which is rather different from actual adjusting).