Rtorrent

Add trackers to a torrent

Select the torrent. Press Ctrl+x and insert this command:

d.tracker.insert="3","url_of_tracker"

where 3 is the next slot in the tracker list (usually 1 is occupied by the site the torrent was downloaded from and 2 by dht) and url_of_tracker is obviously the url of the new tracker. Might be necessary to do a tracker update request with T (or just wait a bit and rtorrent will do it by itself)