Sub DemoChangeDelimiters()
 Dim str As String
 str = QuickRead(ThisWorkbook.Path & "\book1.csv")
 str = Replace(str, ",", ";")
 QuickWrite str, ThisWorkbook.Path & "\book1.csv", True
End Sub

' Reads a file into a string.
Function QuickRead(fname As String) As String
 Dim i As Integer, res As String, l As Long
 ' Get a free file handle.
 i = FreeFile
 ' Get the length of the file
 l = FileLen(fname)
 ' Create a string to contain the data.
 res = Space(l)
 ' Open the file.
 Open fname For Binary Access Read As #i
 ' Read the whole file into res.
 Get #i, , res
 ' Close the file
 Close i
 ' Return the string.
 QuickRead = res
End Function

' Writes data to a file.
Function QuickWrite(data As String, fname As String, _
 Optional overwrite As Boolean = False) As Boolean
 Dim i As Integer, l As Long
 ' If file exists and overwrite is True, then
 If Dir(fname) <> "" Then
 If overwrite Then
 ' delete the file.
 Kill fname
 Else
 ' else, return False and exit.
 QuickWrite = False
 Exit Function
 End If
 End If
 ' Get a free file handle.
 i = FreeFile
 ' Get the length of the file
 l = Len(data)
 ' Open the file.
 Open fname For Binary Access Write As #i Len = l
 ' Read the whole file into res.
 Put #i, , data
 ' Close the file
 Close i
 ' Return True.
 QuickWrite = True
End Function