PrefabUtility.ReplacePrefab

Description

Replaces the targetPrefab with a copy of the game object hierarchy go.

Returns the prefab game object after it has been created. If connectToPrefab is enabled go will be made an instance of the created prefab.

// Creates a prefab from the selected GameObjects.
// If the prefab already exists it asks if you want to replace it.

using UnityEngine;
using UnityEditor;

public class ExampleClass : EditorWindow
{
    [MenuItem("Examples/Create Prefab From Selected")]
    static void CreatePrefab()
    {
        GameObject[] objs = Selection.gameObjects;

        foreach (GameObject go in objs)
        {
            string localPath = "Assets/" + go.name + ".prefab";
            if (AssetDatabase.LoadAssetAtPath(localPath, typeof(GameObject)))
            {
                if (EditorUtility.DisplayDialog("Are you sure?",
                        "The prefab already exists. Do you want to overwrite it?",
                        "Yes",
                        "No"))
                {
                    CreateNew(go, localPath);
                }
            }
            else
            {
                CreateNew(go, localPath);
            }
        }
    }

    // Disable the menu item if no selection is in place
    [MenuItem("Examples/Create Prefab From Selected", true)]
    static bool ValidateCreatePrefab()
    {
        return Selection.activeGameObject != null;
    }

    static void CreateNew(GameObject obj, string localPath)
    {
        Object prefab = PrefabUtility.CreateEmptyPrefab(localPath);
        PrefabUtility.ReplacePrefab(obj, prefab, ReplacePrefabOptions.ConnectToPrefab);
    }
}