SetVolumeAlphaEditor.cs

//This file must go in Assets/Editor to function!

using UnityEngine;
using System.Collections;
using UnityEditor;

[CustomEditor(typeof(SetVolumeAlpha))]
public class SetVolumeAlphaEditor : Editor
{
    public override void OnInspectorGUI()
    {
        DrawDefaultInspector();

        SetVolumeAlpha myScript = (SetVolumeAlpha)target;
        if (GUILayout.Button("Set Alpha (Chunk Refresh required)"))
        {
            myScript.SetAlpha();
        }
    }
}