unity, add object to asset and remove object from asset

//----create a scriptable object and add it to an existing asset
                    CmyScriptableObject obj = ScriptableObject.CreateInstance<CmyScriptableObject> ();
                    AssetDatabase.AddObjectToAsset(obj,existingAsset);

// Reimport the asset after adding an object.
                    // Otherwise the change only shows up when saving the project
                    AssetDatabase.ImportAsset(AssetDatabase.GetAssetPath(obj));

Selection.activeObject = obj;

//----remove object in asset

//ref : http://answers.unity3d.com/questions/219465/how-can-i-remove-an-object-from-an-asset.html

UnityEngine.Object.DestroyImmediate(obj, true);
                    AssetDatabase.SaveAssets();