Change Attribute's parameter at runtime

Well you learn something new every day, apparently I lied:

What isn’t generally realised is that you can change attribute instance values fairly easily at runtime. The reason is, of course, that the instances of the attribute classes that are created are perfectly normal objects and can be used without restriction. For example, we can get the object:

ASCII[] attrs1=(ASCII[])
    typeof(MyClass).GetCustomAttributes(typeof(ASCII), false);

…change the value of its public variable and show that it has changed:

attrs1[0].MyData="A New String";
MessageBox.Show(attrs1[0].MyData);

…and finally create another instance and show that its value is unchanged:

ASCII[] attrs3=(ASCII[])
    typeof(MyClass).GetCustomAttributes(typeof(ASCII), false);
 MessageBox.Show(attrs3[0].MyData);

http://www.vsj.co.uk/articles/display.asp?id=713

In case anyone else walks down this avenue, the answer is you can do it, with reflection, except you can't because there's a bug in the framework. Here's how you would do it:

Dim prop As PropertyDescriptor = TypeDescriptor.GetProperties(GetType(UserInfo))("Age")
Dim att As CategoryAttribute = DirectCast(prop.Attributes(GetType(CategoryAttribute)), CategoryAttribute)
Dim cat As FieldInfo = att.GetType.GetField("categoryValue", BindingFlags.NonPublic Or BindingFlags.Instance)
cat.SetValue(att, "A better description")

All well and good, except that the category attribute is changed for all the properties, not just 'Age'.