Is it possible to change CustomPass variables via other script?

Is it possible to set/get a variable used in a CustomPassVolume component? I tried just using GetComponent<[CustomPassName]>() but that didn't work because apparently GetComponent only works on MonoBehaviour components. I also tried using an interface:

 public interface ICustomPassVariables {
     Transform transform {
         get; set;
     }
 }

and implementing it like this:

 class [CustomPassName] : CustomPass, ICustomPassVariables {
 .
 .
     public Transform transform {
         get {
             return target;
         }
         set {
             target = value;
         }
     }
 .
 .
 }

And using it in the other script like this:

 ICustomPassVariables customPassVariables = volume.gameObject.GetComponent<ICustomPassVariables>();
 customPassVariables.transform = transform;

But that just resulted in a NullReferenceException. I tried other methods to get the interface component referenced here but it still resulted in a NullReferenceException. We can change the variables in the inspector so there has to be a way to do so by script right? Thank you.