Hi anon, is it possible to tell biglybt to use custom key and port values?
Yes and no. You can't directly tell it to use a custom key and port, but you can alter your client file to hardcode those values (example: uTorrent, with changes highlighted).
<query staticNumwant="200" ipType="2" ipMode="1" ipFallBack="0">
<param>[info_hash]</param>
<param>[peer_id]</param>
<param>&port=12345</param>
<param>[uploaded]</param>
<param>[downloaded]</param>
<param>[left]</param>
<param>[corrupt]</param>
<param>&key=1234ABCD</param>
<param>{event}</param>
<param>[numwant]</param>
<param>[compact]</param>
<param>[no_peer_id]</param>
</query>
However, if you restart the real client, you have to close the mod, obtain the new values, re-edit the client file to make them match, and start the mod again.