How can I transform Magnet links to .torrent format?

How to convert magnet to torrent file

You shouldn't have issues trying to convert Magnet links directly to BitTorrent files (magnet to torrent conversion) since there are various BitTorrent tools and online converters supporting such efforts.

It seems your best bet would be using tools such as uTorrent and Vuze, which should let you convert Magnet Links to BitTorrent Files easily.

Alternatively, you will find several online conversion utilities capable of such conversion.