Binaryworld - ChangeFileExtension - Modify the extension in a file name ... [ VB -> Files & Folder ]

' Change the extension of a file name
' if the last argument is True, it adds the extension even if the file doesn't
' have one

Function ChangeFileExtension(FileName As String, Extension As String, _
  Optional AddIfMissing As Boolean) As String
  Dim i As Long
  For i = Len(FileName) To 1 Step -1
    Select Case Mid$(FileName, i, 1)
      Case "."
        ' we've found an extension, so replace it
        ChangeFileExtension = Left$(FileName, i) & Extension
        Exit Function
      Case ":", "\"
        Exit For
    End Select
  Next

  ' there is no extension
  If AddIfMissing Then
    ChangeFileExtension = FileName & "." & Extension
  Else
    ChangeFileExtension = FileName
  End If
End Function