</asp:TemplateField><asp:TemplateField HeaderText="FREQUENCY:">
<ItemTemplate>
<asp:Label ID="lblFreq" runat="server" Text='<%# ChangeEval(Eval("Frequency")) %>' />
</ItemTemplate>
</asp:TemplateField>
You can add custom binding for your control, now in aspx.cs page Implement
ChangeEval
for example
public object ChangeEval(object evalValue)
{
if(evalValue.Tostring()=="D")
return "DAY";
else if(....)
return ...
....
}