Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
 
        Dim startindex As Integer = 5 'Start des Einfügens
        Dim str, str2 As String
        With ListBox2
            If .SelectedItem Is Nothing Then Exit Sub
            str = CType(.SelectedItem, String)
        End With
 
        With ListBox1
            For i As Integer = 0 To .Items.Count - 1
                str2 = CType(.Items(i), String)
                If str2.Length > 5 Then
                    .Items(i) = str2.Insert(startindex, str)
                End If
            Next i
        End With
    End Sub