See the question and my original answer on StackOverflow

What you could do is reuse the DynamicTypeDescriptor class described in my answer to this question here on SO: PropertyGrid Browsable not found for entity framework created property, how to find it?

like this:

  public Form1()

      Person p = new Person();

      DynamicTypeDescriptor dt = new DynamicTypeDescriptor(typeof(Person));
      propertyGrid1.SelectedObject = dt.FromComponent(p);

  private void button1_Click(object sender, EventArgs e)
      DynamicTypeDescriptor dt = (DynamicTypeDescriptor)propertyGrid1.SelectedObject;
      DynamicTypeDescriptor.DynamicProperty dtp = (DynamicTypeDescriptor.DynamicProperty)dt.Properties["Age"];

      dtp.SetDisplayName("The age");
      dtp.SetDescription("Age of the person");