Bukkit

Well both things are already explaining themselves.

Spread Fall:
As longer as you shoot the Spread will increase or decrease
The Module for it:

Spread_Fall:
Enabled: true
Spread_Increase: false (If you want to make to increase the Accuracy if shooting or decrease it)
After_Shoot: 2 (After which Shots theSpread should start Increase or decrease)
Refresh_Spread_After: 20 (Value in Ticks, This is the time when the Spread refreshes to it's original Value

The Knockback:
If you shot a Guy he gets knocked back but if you shoot him with an Automatic Gun he is like flying. You should redo the "Knockback" under Abilities if you set Knockback: 0 it should deal no knockback.

Your request is being asked thousand times and Shampaggon never tried to implement them. I think he do not want to implement these to not Crackshot being broken on every Minecraft updates.