This script migrates the "old" layout format to the new format used in Sitecore 8.2 Update-7 and Sitecore 9 Update-2. Code from: https://sitecore.namics.com/upgrading-to-sitecore-9-0-update-2-and-later-versions-might-change-the-order-of-renderings/ updated to use ID rather than path

MigrateLayouts.aspx

<%@ Page Language="C#" AutoEventWireup="true" Debug="true" %>
<%@ Import Namespace="System.Linq" %>
<%@ Import Namespace="Sitecore" %>
<%@ Import Namespace="Sitecore.Configuration" %>
<%@ Import Namespace="Sitecore.Data" %>
<%@ Import Namespace="Sitecore.Data.Fields" %>
<%@ Import Namespace="Sitecore.Data.Items" %>
<%@ Import Namespace="Sitecore.Globalization" %>
<%@ Import Namespace="Sitecore.Layouts" %>

<script language="C#" runat="server">

    /// https://sitecore.namics.com/upgrading-to-sitecore-9-0-update-2-and-later-versions-might-change-the-order-of-renderings/
    /// <summary>
    /// This script migrates the "old" layout format to the new format used in Sitecore 8.2 Update-7 and Sitecore 9 Update-2.
    /// Sitecore Knowledge Base article: https://kb.sitecore.net/articles/672981
    /// 
    /// GET Parameters
    /// - database: The Sitecore database the script should run on. Example: master
    /// - itemId: The dynamic placeholder migration is only processed on this start item. Example: {456B38B8-1C42-48AF-858E-FC58A2FC1491}
    /// - enableRecursion: This option enables recursion for the start item. Example: true
    /// </summary>

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Sitecore.Context.User.IsAdministrator)
        {
            Response.Write("You have no permission to run this script.");
            return;
        }

        var databaseName = Context.Request.QueryString["database"];
        if (string.IsNullOrEmpty(databaseName))
        {
            databaseName = "master";
        }

        var database = Factory.GetDatabase(databaseName);

        ID startItemId = null;
        Item startItem = null;
        var startItemIdString = Context.Request.QueryString["itemId"];

        if (string.IsNullOrEmpty(startItemIdString))
        {
            Response.Write("No Item ID provided. Please use GET parameter 'itemId'.");
            return;
        }

        if (!string.IsNullOrEmpty(startItemIdString) &&
            !Sitecore.Data.ID.TryParse(startItemIdString, out startItemId))
        {
            Response.Write("Invalid Item ID.");
            return;
        }

        if (!string.IsNullOrEmpty(startItemIdString))
        {
            startItem = database.GetItem(startItemId);
        }

        if (!string.IsNullOrEmpty(startItemIdString) && startItem == null)
        {
            Response.Write(string.Format("No item found for ID {0}.", startItemIdString));
            return;
        }

        bool isRecursionEnabled;
        bool.TryParse(Context.Request.QueryString["enableRecursion"], out isRecursionEnabled);

        var fixRenderings = new UpgradeLayoutHelper(database);

        Sitecore.Diagnostics.Log.Info("Layout Migration: Started", this);

        fixRenderings.Iterate(startItem, isRecursionEnabled);

        Sitecore.Diagnostics.Log.Info("Layout Migration: Finished", this);
    }

    public class UpgradeLayoutHelper
    {
        private const string ItemsWithPresentationDetailsQuery =
            "{0}//*[@__Renderings != '' or @__Final Renderings != '']";

        private readonly Database _database;

        public UpgradeLayoutHelper(Database database)
        {
            _database = database;
        }

        public Dictionary<Item, List<KeyValuePair<string, string>>> Iterate(Item startItem, bool isRecursionEnabled)
        {
            var result = new Dictionary<Item, List<KeyValuePair<string, string>>>();

            var items = new List<Item>();

            if (startItem != null)
            {
                items.Add(startItem);

                if (isRecursionEnabled)
                {
                    items.AddRange(_database.SelectItems(string.Format(ItemsWithPresentationDetailsQuery,
                        startItem.ID)));
                }
            }
            else
            {
                items.AddRange(
                    _database.SelectItems(string.Format(ItemsWithPresentationDetailsQuery, "/sitecore/content")));
            }

            foreach (var itemInDefaultLanguage in items)
            {
                UpdateLayoutField(itemInDefaultLanguage);
            }

            return result;
        }

        public void UpdateLayoutField(Item item)
        {
            bool isSharedLayoutFieldUpdated = false;

            foreach (var language in item.Languages)
            {
                Item itemInLanguage = _database.GetItem(item.ID, language);
                if (itemInLanguage.Versions.Count > 0)
                {
                    foreach (Item itemVersion in itemInLanguage.Versions.GetVersions())
                    {
                        foreach (Field f in itemVersion.Fields)
                        {
                            if (f.ID == FieldIDs.FinalLayoutField)
                            {
                                itemVersion.Editing.BeginEdit();
                                string fieldValue = Sitecore.Data.Fields.LayoutField.GetFieldValue(itemVersion.Fields[FieldIDs.FinalLayoutField]);
                                LayoutField.SetFieldValue(f, fieldValue);
                                itemVersion.Editing.EndEdit();
                            }
                        }

                        if (!isSharedLayoutFieldUpdated)
                        {
                            foreach (Field f in itemVersion.Fields)
                            {
                                if (f.ID == FieldIDs.LayoutField)
                                {
                                    itemVersion.Editing.BeginEdit();
                                    string fieldValue = LayoutField.GetFieldValue(itemVersion.Fields[FieldIDs.LayoutField]);
                                    LayoutField.SetFieldValue(f, fieldValue);
                                    itemVersion.Editing.EndEdit();

                                    isSharedLayoutFieldUpdated = true;
                                }
                            }
                        }
                    }
                }
            }
        }
    }


</script>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
<form id="form1" runat="server">
    <div>
        Done.

    </div>
</form>
</body>
</html>