Addition Quaternion

I have a gun, this gun is basically a cylinder and with a sphere inside. The sphere is a child of the gun, so want ever rotation the gun is the sphere is. I have a script so when you press 'Z', it spawns the sphere in the direction of the gun is pointing. Now this rotation is very important to understand.

I want to add something into the script so the direction is slightly offset, you known to simulate caliber but I want to keep the general direction of the sphere. The gun is going to be moving and rotating so it is important to know that.

I was think something like '+ Random. Range(1,100)'? However you can't add integers to quaternions.

Here's the script:

 #pragma strict
 var ball : GameObject;
 var rotation : Quaternion = transform.rotation;
 function Start () {   
 }
 function Update () {
     if (Input.GetKeyDown(KeyCode.Z)){
         Instantiate(ball,transform.position,transform.rotation);
     }   
 }