Unity Editor Tool to attempt replace selected GameObjects with any asset matching the name of selected.

Replacer.cs

using UnityEngine;
using UnityEditor;

public class Replacer : EditorWindow
{
    [MenuItem("Window/Replacer")]
    public static void ShowWindow()
    {
        EditorWindow.GetWindow<Replacer>("Replace GameObject");
    }

    private void OnGUI()
    {
        GUI.skin.label.wordWrap = true;

        string instructions = "Select GameObjects to be replaced, script will go through each selected " +
            " GameObject and check it is active in Hierarchy, then find path to the asset and instansiate " +
            "it - set Transform and Parent to be same as selection and destroy the old one.\n\n" +
            "Known issues; \n\n" +
            "   - Only works if GameObject hasn't been renamed.\n";

        GUILayout.Label("Instructions", EditorStyles.boldLabel);
        GUILayout.Label(instructions);

        if (GUILayout.Button("Replace Selected GameObjects"))
        {
            GameObject[] selection = Selection.gameObjects;
            foreach (GameObject item in selection)
            {
                if (item.activeInHierarchy)
                {
                    // TODO: Refactor so we can avoid this nested chaos.
                    // TODO: Solve path to renamed GameObjects

                    string[] guids = AssetDatabase.FindAssets(GetObjectName(item.name));

                    if (guids.Length > 0)
                    {
                        string path = AssetDatabase.GUIDToAssetPath(guids[0]);
                        GameObject asset = Instantiate(AssetDatabase.LoadAssetAtPath<GameObject>(path));
                        Replace(item, asset);
                    }
                }  
            }
        }
    }

    /// <summary>
    /// Splits a string on spaces and return first string in resulting string array.
    /// </summary>
    /// <param name="NameInHierarchy"></param>
    /// <returns></returns>
    private string GetObjectName(string NameInHierarchy) {
        return NameInHierarchy.Split(' ')[0];
    }

    /// <summary>
    /// Replace oldGameObject with newGameObject, copying over transform information
    /// and name.
    /// </summary>
    /// <param name="oldGameObject"></param>
    /// <param name="newGameObject"></param>
    private void Replace(GameObject oldGameObject, GameObject newGameObject)
    {
        newGameObject.transform.parent = oldGameObject.transform.parent;

        newGameObject.transform.SetPositionAndRotation(
            oldGameObject.transform.position,
            oldGameObject.transform.rotation
        );

        newGameObject.transform.localScale = oldGameObject.transform.localScale;

        string name = oldGameObject.name;

        DestroyImmediate(oldGameObject);

        newGameObject.name = name;
    }
}