Вот простой пример установки текста с помощью кода-позади.
Front-End HTML
<form id="form1" runat="server">
<div>
<asp:Literal ID="ltlTest" runat="server" />
</div>
</form>
Code-Behind
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Me.ltlTest.Text = String.Format("Line 1 {0} Line 2 {0} Line 3 {0} Line 4", "<br />")
End Sub