ReplacerWizard.cs

using UnityEditor;
using UnityEngine;

public class ReplacerWizard : ScriptableWizard
{
	[SerializeField] private GameObject prefab = null;

	[MenuItem("Tools/Replacer")]
	static void CreateWizard()
	{
		DisplayWizard<ReplacerWizard>("Replace GameObjects", "Replace");
	}

	void OnWizardCreate()
	{
		Undo.SetCurrentGroupName("Replace");
		foreach (var oldObject in Selection.GetFiltered<GameObject>(SelectionMode.ExcludePrefab))
		{
			GameObject newObject = (GameObject)PrefabUtility.InstantiatePrefab(prefab);
			newObject.transform.parent = oldObject.transform.parent;
			newObject.transform.localPosition = oldObject.transform.localPosition;
			newObject.transform.localRotation = oldObject.transform.localRotation;
			newObject.transform.localScale = oldObject.transform.localScale;
			Undo.RegisterCreatedObjectUndo(newObject, "Instantiate " + newObject.name);
			Undo.DestroyObjectImmediate(oldObject);
		}
	}

	void OnWizardUpdate()
	{
		helpString = "Choose a prefab with which to replace all selected GameObjects";
		isValid = prefab && !prefab.scene.IsValid();
		errorString = isValid ? "" : "Select a prefab from Assets";
	}
}