type value in the weapon knockback functions can be 0 or 1. If 0, the value becomes an absolute distance that targets will be knocked back. If 1, the value is multiplied by the distance they would normally have been knocked back. Weapon knockback modifiers are applied in the order weapon -> attacker -> target, so a x2 weapon wielded by an abs 6 attacker hitting a /2 target will knock the target back 3 squares. The knockback functions will not override the stonewall perk or knockdowns resulting from criticals. knockback values set on weapons or critters are not saved, and must be reset each time the player reloads.
void set_attacker_knockback(CritterPtr, int type, float value)
void set_target_knockback(CritterPtr, int type, float value)
void set_weapon_knockback(WeaponPtr, int type, float value)