Dim F As Integer
Dim sInhalt As String
Dim I As Long
 
F = FreeFile
Open "DeineDatei.txt" For Binary As #F
sInhalt = Space$(Lof(F))
Get #F, , sInhalt
Close #F
 
For I = 1 To Len(sInhalt)
  If Mid$(sInhalt, I, 1) = "." Then
    Mid$(sInhalt, I, 1) = ","
  ElseIf Mid$(sInhalt, I, 1) = "," Then
    Mid$(sInhalt, I, 1) = "."
  End If
Next I
 
F = FreeFile
Open "DeineDatei.txt" For Output As #F
Print #F, sInhalt;
Close #F