Populate a template with ExcelTemplate and then programmatically manipulate or 'post process' the workbook with ExcelApplication.

private ExcelTemplate xlt;
private ExcelApplication xlw;
private Workbook wb;


	/// <summary>
        /// Build the report with ExcelApplication
        /// </summary>
        public void GenerateReport()
        {
            
            PopulateTemplate();
            AddChart();

            /* Save the report to specified folder */
            xlw.Save(wb, @"..\..\Output\TempToApp_output.xlsx");
        }

        /// <summary> Add a column chart to the second worksheet using ExcelApplication.
        /// The chart will show data imported with the ExcelTemplate
        /// object.</summary>
        private void AddChart()
        {
            /* Get the first two worksheets and give them names */
            Worksheet ws = wb.Worksheets[0];
            ws.Name = "Data";

            Worksheet ws2 = wb.Worksheets.CreateWorksheet("ChartSheet");

            /* Create a chart on the second worksheet */
            Anchor anch = ws2.CreateAnchor(0, 0, 50, 50);
            Chart chrt = ws2.Charts.CreateChart(ChartType.Column.Clustered, anch);

            /* Set series and category data */
            Series srs1 = chrt.SeriesCollection.CreateSeries("=Data!B2:B7");
            chrt.SeriesCollection.CategoryData = "=Data!A2:A7";
            srs1.NameFormula = "=Data!A1";

            /* Configure the chart's legend */
            Legend lgnd = chrt.Legend;
            lgnd.Visible = true;
            lgnd.Location = Legend.LegendLocation.Right;

            /* Set the chart's Title string and display properties. */
            chrt.Title.Text = "AdventureWorks Global Sales";
        }