Unity3D Guid Saving

GuidComponent.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

#if UNITY_EDITOR
using UnityEditor;
#endif

/*
 * Saves custom GUID for a gameobject. Will automatically make sure
 * there are no duplicates. Checks open scenes as well as prefabs
 * By default, GUID is not saved when inside of a prefab asset.
 */
[ExecuteInEditMode, DisallowMultipleComponent]
public class GuidComponent : MonoBehaviour, ISerializationCallbackReceiver
{
    //Cached Value
    private System.Guid guid = System.Guid.Empty;

    [SerializeField]
    private byte[] serializedGuid;

    //Whether to clear GUID's when this object is in a prefab asset
    //If true, instantiating this object will create a new GUID. Otherwise,
    //it will retain the GUID from before.
    [SerializeField]
    public bool clearIfPrefabAsset = true;

    public System.Guid Guid
    {
        get
        {
            return guid;
        }
        set
        {
            guid = value;
            serializedGuid = guid.ToByteArray();
        }
    }

    public string GuidString
    {
        get { return Guid.ToString(); }

        set { Guid = new System.Guid(value); }
    }

    private bool DisableSerialization()
    {
#if UNITY_EDITOR
        return (clearIfPrefabAsset && PrefabUtility.IsPartOfPrefabAsset(this));
#else
        return false;
#endif
    }

    public void OnAfterDeserialize()
    {
        if (serializedGuid != null && serializedGuid.Length == 16)
            guid = new System.Guid(serializedGuid);

    }

    public void OnBeforeSerialize()
    {
#if UNITY_EDITOR
        if (DisableSerialization())
        {
            serializedGuid = null;
            guid = System.Guid.Empty;
        }
#endif
    }

    public void CreateGuid()
    {
        Guid = System.Guid.NewGuid();

#if UNITY_EDITOR
        if(!Application.isPlaying)
        {
            Undo.RecordObject(this, "GUID Creation");

            if (PrefabUtility.IsPartOfVariantPrefab(this))
                PrefabUtility.RecordPrefabInstancePropertyModifications(this);

            UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(gameObject.scene);

        }
#endif
    }

    void Awake()
    {

        //Automatically create a GUID if it is empty / invalid
        if(serializedGuid == null || serializedGuid.Length != 16)
        {
            if (!DisableSerialization())
                CreateGuid();
            return;
        }

#if UNITY_EDITOR

        if (Application.isPlaying)
            return;

        //Scan all guid components
        bool foundDuplicate = false;
        foreach(GuidComponent gc in Resources.FindObjectsOfTypeAll<GuidComponent>())
        {
            if (gc == this)
                continue;

            if(gc.Guid.ToString() == Guid.ToString())
            {
                foundDuplicate = true;
                break;
            }
        }

        if(foundDuplicate)
            CreateGuid();

#endif
    }
}

GuidComponentInspector.cs

using UnityEditor;

[CustomEditor(typeof(GuidComponent))]
class GuidComponentInspector : Editor
{
    public override void OnInspectorGUI()
    {
        GuidComponent guidComp = (GuidComponent)target;
        EditorGUILayout.SelectableLabel(guidComp.Guid.ToString());

    }

}