I would like to provide magnet links in my service, for large downloadable files. However, I would like to be able to tell the Torrent-download client only to grab a specific file within the torrent/magnet. Is this possible and how can it be done?
You would need to create separate torrents for each set of files you want, then spawn magnet links for each.
As far as I have seen there are no switches you can include in magnet link that will define intra-torrent settings. Even if it could, there would be no guarantee the client would recognize and obey those commands.