You can change the URL of each provider to point to a custom location. However, note that not all mirror sites with the same name have the exact same underlying website. Although many of the torrent sites have proxies and may look very similar, they often do not share the same HTML structure and syntax. The provider code implemented in Gaia might therefore not work for your custom site. You have to test and find out.
To customize the provider's location, go to: Gaia → Settings → Providers
Last Updated: 06 Jan 2018