Visual Basic.NET - Cambiar Valores de una key de App.Config

Public Class Class1

    Private Shared aReaderSettings As New System.Configuration.AppSettingsReader

    Private Shared myRuns As String _

    = aReaderSettings.GetValue("cRuns", GetType(String))

    Public Shared ReadOnly Property cRuns() As String

        Get

            Return myRuns

        End Get

    End Property

End Class

Imports System.Configuration

Imports System.Configuration.ConfigurationSettings

Public Class Form1

    Dim a As Integer

    Dim Runs As Integer

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        a = 0

        Label2.Text = Class1.cRuns

    End Sub

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

        a = a + 1

        Label1.Text = a

        Label2.Text = Class1.cRuns - a

    End Sub

    Private Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click

        a = a - 1

        Label1.Text = a

        Label2.Text = Class1.cRuns - a

    End Sub

End Class

<appSettings>

    <add key="cRuns" value="300"/>

  </appSettings>

Dim pluginAssemblyPath As String = Assembly.GetExecutingAssembly().Location

    Dim configuration As Configuration = ConfigurationManager.OpenExeConfiguration(pluginAssemblyPath)

    Dim test1 As String = configuration.AppSettings.Settings.Item("Key1").Value

    configuration.AppSettings.Settings.Item("cRuns").Value = "Is this thing on?"

    Dim test3 As String = configuration.AppSettings.Settings.Item("cRuns").Value

    configuration.AppSettings.SectionInformation.ForceSave = True

    configuration.Save(ConfigurationSaveMode.Modified)

    ConfigurationManager.RefreshSection("appSettings")