Better way way to modify rendered HTML in Asp.net

I found a better a way to modify the HTML in ASP.Net just before it is sent to the client. Here is the code:

public partial class CustomRender : System.Web.UI.Page
{
 HtmlTextWriter textWriter = null;
 StringWriter stringWriter = new StringWriter();

 protected override HtmlTextWriter CreateHtmlTextWriter(TextWriter tw)
 {
 textWriter = base.CreateHtmlTextWriter(tw);
 return base.CreateHtmlTextWriter(stringWriter);
 }
protected override void Render(HtmlTextWriter writer)
 {
base.Render(writer);
 string htmlCode = stringWriter.ToString().Replace("[CurDateTime]", DateTime.Now.ToString());;

 textWriter.Write(textWriter);

 }
}

I used the same .aspx file we used in the last example.