how to programmatically decide which content page to load , on master page load

Question

I have a master page and two content pages with the same ContentPlaceHolderID. Is there a way to specify which content page should be loaded from the Page_Load event of the master page?

If I watch the value of:

Request.CurrentExecutionFilePath;

I see the path of the first content page.

According to the condition specified below i want to change it to the path of the second content page.

I am looking for a way to load a specific page depending on a check I do on the Master Page_Load.

If I attempt to redirect to the page from there I get stuck in an endless loop because the master page loads again before the content page and re-does the check and redirects again and again.

// in master page 
protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        if (Request.Cookies["user"] != null)
        {
            HttpCookie cookie = Request.Cookies["user"];
            string name = cookie.Value;
            Response.Redirect("~/hello_page.aspx?UserName=" + name);
        }
    }
}

Thanks in advance.