If you are sending file uploads through an API, you may need more file information than just the url.
[25 show=id encoding=base64] will return the file contents
[25 show=id pathinfo=basename] will return the filename
[25 show=id fileinfo=mimetype] will return the MIME type

Use this code to change the name of the exported CSV file(s) for a particular form. Remove the if statement (line 3) and the } before "return $filename" in order to the change the name of exported CSV files for all forms.