Replace objects with a prefab

ReplaceWithPrefab.cs

using UnityEditor;
using UnityEngine;

public class ReplaceWithPrefabWindow : EditorWindow
{
    public Transform prefab;

    [MenuItem("GameObject/Replace with prefab")]
    static void Init()
    {
        // Get existing open window or if none, make a new one:
        ReplaceWithPrefabWindow window = (ReplaceWithPrefabWindow)EditorWindow.GetWindow(typeof(ReplaceWithPrefabWindow));
        window.titleContent = new GUIContent("Replace with prefab");
        window.Show();
    }

    void OnGUI()
    {
        GUILayout.Label("Replacement prefab", EditorStyles.boldLabel);
        prefab = (Transform)EditorGUILayout.ObjectField(prefab, typeof(Transform), false);
        if (prefab != null && GUILayout.Button("Replace Selection"))
        {
            int group = Undo.GetCurrentGroup();
            Undo.SetCurrentGroupName("Undo replace objects with prefab");
            foreach (var selectedObject in Selection.gameObjects)
            {
                Transform replacement = (Transform)PrefabUtility.InstantiatePrefab(prefab);
                Undo.RegisterCreatedObjectUndo(replacement.gameObject, "replacement prefab");
                Undo.SetTransformParent(replacement, selectedObject.transform.parent, "set parent");
                replacement.name = selectedObject.name;
                replacement.position = selectedObject.transform.position;
                replacement.rotation = selectedObject.transform.rotation;
                replacement.localScale = selectedObject.transform.localScale;
                int siblingNumber = selectedObject.transform.GetSiblingIndex();
                Undo.DestroyObjectImmediate(selectedObject);
                replacement.SetSiblingIndex(siblingNumber);
            }
            Undo.CollapseUndoOperations(group);
        }
    }
}