AddChildInAsset and AddChildInAssetWithComponent<T>

gistfile1.cs

public static GameObject AddChildInAsset (GameObject prefab, string name = "NewChild")
{
	GameObject instance = (GameObject)PrefabUtility.InstantiatePrefab (prefab);
	GameObject child = AddChild (instance, System.Guid.NewGuid ().ToString ());
	PrefabUtility.ReplacePrefab (instance, prefab, ReplacePrefabOptions.ConnectToPrefab);
	GameObject newChild = prefab.transform.FindChild (child.name).gameObject;
	GameObject.DestroyImmediate (instance);
	newChild.name = name;
	prefab.MakeDirty ();
	AssetDatabase.SaveAssets ();
	AssetDatabase.Refresh ();
	Debug.Log ("Child Created in Asset: " + newChild.name);
	return newChild;
}
public static T AddChildInAssetWithComponent<T> (GameObject prefab, string name = "NewChild") where T : Component
{
	GameObject newChild = AddChildInAsset (prefab, name);
	T newComponent = newChild.AddComponent<T> ();
	return newComponent;
}