Me.Usercontrol1.Textbox1.Text="Beispieltext"

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles TextBox1.TextChanged
        '
        ' Deine Aktionen
        '
End Sub
End Class

Public Class UserControl1
 
    Public Event MyOwnTextboxTextChangedEvent(ByVal sender As Object, ByVal e _
      As System.EventArgs)
 
    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles TextBox1.TextChanged
        '
        'Deine Aktionen
        '
        RaiseEvent MyOwnTextboxTextChangedEvent(sender, e)
 
    End Sub
 
End Class

    Private Sub UserControl11_MyOwnTextboxTextChangedEvent(ByVal sender As _
      Object, ByVal e As System.EventArgs) Handles _
      UserControl11.MyOwnTextboxTextChangedEvent
        Dim MyUsercontrolTextBox = CType(sender, TextBox)
    End Sub

MyUsercontrolTextBox