(UnityEngine) Replaces object with specified prefab (Keeps transform). Useful for prototyping.

ReplaceWithPrefab.cs

using UnityEngine;
using UnityEditor;

public class ReplaceWithPrefab : EditorWindow
{
    [SerializeField] private int lenght;
    public int Lenght
    {
        get => lenght;
        set
        {
            lenght = value;
            if (value != 0)
            {
                GameObject[] buffer = _gameObjects;
                _gameObjects = new GameObject[lenght];
                for (int i = 0; i < lenght; i++)
                {
                    if (buffer.Length > i)
                        _gameObjects[i] = buffer[i];
                    else
                        _gameObjects[i] = null;
                }
            }
        }
    }

    private GameObject[] _gameObjects;

    [MenuItem("Tools/Replace With Prefab")]
    static void CreateReplaceWithPrefab()
    {
        EditorWindow.GetWindow<ReplaceWithPrefab>();
    }

    private void OnGUI()
    {
        Lenght = EditorGUILayout.IntField("Prefab count: ", Lenght);
        for (int j = 0; j < Lenght; j++)
        {
            GUILayout.BeginHorizontal();
            _gameObjects[j] = (GameObject)EditorGUILayout.ObjectField(_gameObjects[j], typeof(GameObject), false);
            if (GUILayout.Button("Replace"))
            {
                var selection = Selection.gameObjects;

                for (var i = selection.Length - 1; i >= 0; --i)
                {
                    var selected = selection[i];
                    GameObject newObject;

                    if (PrefabUtility.IsPartOfPrefabAsset(_gameObjects[j]))
                    {
                        newObject = (GameObject)PrefabUtility.InstantiatePrefab(_gameObjects[j]);
                    }
                    else
                    {
                        newObject = Instantiate(_gameObjects[j]);
                        newObject.name = _gameObjects[j].name;
                    }

                    if (newObject == null)
                    {
                        Debug.LogError("Error instantiating prefab");
                        break;
                    }

                    Undo.RegisterCreatedObjectUndo(newObject, "Replace With Prefabs");
                    newObject.transform.parent = selected.transform.parent;
                    newObject.transform.localPosition = selected.transform.localPosition;
                    newObject.transform.localRotation = selected.transform.localRotation;
                    newObject.transform.localScale = selected.transform.localScale;
                    newObject.transform.SetSiblingIndex(selected.transform.GetSiblingIndex());
                    Undo.DestroyObjectImmediate(selected);
                }
            }
            
            GUILayout.EndHorizontal();
        }
        
        GUI.enabled = false;
        EditorGUILayout.LabelField("Selection count: " + Selection.objects.Length);
    }
}