Altering a Table - Add Identity Column

BEGIN TRY;
    BEGIN TRANSACTION;

    /*Using DBCC CHECKIDENT('dbo.tblFoo') is slow so use dynamic SQL to
      set the correct seed in the table definition instead*/
    DECLARE @TableScript nvarchar(max)
    SELECT @TableScript = 
    '
    CREATE TABLE dbo.Destination(
        bar INT IDENTITY(' + 
                     CAST(ISNULL(MAX(bar),0)+1 AS VARCHAR) + ',1)  PRIMARY KEY,
        filler CHAR(8000),
        filler2 CHAR(49)
        )

        ALTER TABLE dbo.tblFoo SWITCH TO dbo.Destination;
    '       
    FROM dbo.tblFoo
    WITH (TABLOCKX,HOLDLOCK)

    EXEC(@TableScript)

    DROP TABLE dbo.tblFoo;

    EXECUTE sp_rename N'dbo.Destination', N'tblFoo', 'OBJECT';

    COMMIT TRANSACTION;
END TRY
BEGIN CATCH
    IF XACT_STATE() <> 0 ROLLBACK TRANSACTION;
    PRINT ERROR_MESSAGE();
END CATCH;

--replace the real table names 
--delete the PRIMARY KEY
--warning in some ways, maybe need PRIMARY KEY NONCLUSTERED
BEGIN TRY;
    BEGIN TRANSACTION;

    /*Using DBCC CHECKIDENT('dbo.tblFoo') is slow so use dynamic SQL to
      set the correct seed in the table definition instead*/
    DECLARE @TableScript nvarchar(max)
    SELECT @TableScript = 
    '
    CREATE TABLE dbo.COM_ProductsX(
        Product_ID INT IDENTITY(' + 
                     CAST(ISNULL(MAX(Product_ID),0)+1 AS VARCHAR) +',1)  ,[Product_MAINCATEGORY_ID] [int] NULL,[Product_CATEGORY_ID] [int] NULL,[Product_Code] [varchar](50) NULL
        )

        ALTER TABLE dbo.COM_Products SWITCH TO dbo.COM_ProductsX;
    '       
    FROM dbo.COM_Products
    WITH (TABLOCKX,HOLDLOCK)

    EXEC(@TableScript)

    DROP TABLE dbo.COM_Products;

    EXECUTE sp_rename N'dbo.COM_ProductsX', N'COM_Products', 'OBJECT';

    COMMIT TRANSACTION;
END TRY
BEGIN CATCH
    IF XACT_STATE() <> 0 ROLLBACK TRANSACTION;
    PRINT ERROR_MESSAGE();
END CATCH;