Modify tracker URL of transmission tasks.

modtracker.sh

#!/bin/sh

## TODO: Fill the following placeholders:
## USERNAME, PASSWORD
## YOUR_PASSKEY

trr() {
  transmission-remote 127.0.0.1:9091 -n USERNAME:PASSWORD "$@"
}

## Change from default "https://" URL scheme to "http://" URL scheme
my_tracker='http://tracker.hdsky.me/announce.php?passkey=YOUR_PASSKEY'

if [ -z "$1" ]; then
	echo "USAGE: $0 TASK_ID [TASK_ID]"
	exit 1
fi

flag_first=1
for arg; do
	TID="$arg"
	if [ $flag_first = 1 ]; then
		flag_first=0
	else
		echo
	fi

	echo ">> TASK: $TID"
	if trr -t "$TID" -it | sed -e 1d; then
		echo "Changing tracker..."
		trr -t "$TID" -td "$my_tracker"
		trr -t "$TID" -tr 0
		echo "Done"
	else
		echo "$TID: No such task id"
	fi
done

Task ID of transmission tasks can be obtained via:
$ trr -l