Why can't I change Type.Delimiter using Reflection?

If I were to change the value of bool.TrueString, I'd do it using Reflection:

typeof(bool).GetField("TrueString", BindingFlags.Public | BindingFlags.Static).SetValue(null, "Yes");
Console.WriteLine(bool.TrueString); // Outputs "Yes"

However, I cannot manage to change the value of, say, Type.Delimiter:

typeof(Type).GetField("Delimiter", BindingFlags.Public | BindingFlags.Static).SetValue(null, '-');
Console.WriteLine(Type.Delimiter); // Outputs "."

Why is this?