Also, and more importantly, this isn't a preimage attack so replacing an existing torrent's SHA-1 hash with a malicious one isn't computational possible.
A hash collision can still be used as an attack if you create 2 torrents with the same hash and then distribute.
The "good" torrent would not be susceptible to attack via this receiving the entire torrent file directly (say over HTTPS) is fine.
[1] https://torrentfreak.com/the-pirate-bay-dumps-torrents-12022...
Also, and more importantly, this isn't a preimage attack so replacing an existing torrent's SHA-1 hash with a malicious one isn't computational possible.