ModExtension

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