Transmission CLI add trackers in BULK

add_trackers.sh

#!/bin/bash

# I was looking for a way to add/modify all trackers in all torrents in my remote transmission instance.
# So I had bunch of old torrents like 500 of them with mostly broken outdated trackers.
# This is a small helper script that will loop over all your torrents and add trackers that finds on torrentz domain.
# I came out on this: https://github.com/Entware-ng/Entware-ng/wiki/Using-Transmission#adding-more-trackers little script and modify it a bit.
# Please modify this script that it suits your environment.

base_url='https://torrentz2.is'
pattern='announcelist_[0-9]+'

TRANSMISSION_GET_REMOTE_TORRENT_IDS='/usr/bin/transmission-remote REPLACE_WITH_YOUR_TRANSMISSION_URL --netrc /home/REPLACE_WITH_YOUR_HOME/.netrc --ssl -l'
$TRANSMISSION_GET_REMOTE_TORRENT_IDS | while read REMOTE_IDS_LINE
do

    TORRENT_ID=$(echo $REMOTE_IDS_LINE | awk '{print $1}')
    TORRENT_ID=$(echo $TORRENT_ID | sed 's/[^0-9]*//g')

    if [ -n "$TORRENT_ID" ]; then
        TORRENT_ID=$(($TORRENT_ID + 0))
        TRANSMISSION_GET_REMOTE_TORRENT_HASH="$(/usr/bin/transmission-remote REPLACE_WITH_YOUR_TRANSMISSION_URL --netrc /home/REPLACE_WITH_YOUR_HOME/.netrc --ssl -t $TORRENT_ID -i)"
        TR_TORRENT_HASH=$(echo $TRANSMISSION_GET_REMOTE_TORRENT_HASH | grep -o -P '(?<=Hash:).*(?=Magnet:)' | grep '[[:xdigit:]]\{32\}')
        TR_TORRENT_HASH="$(echo -e "${TR_TORRENT_HASH}" | tr -d '[:space:]')"

        PERCENT_DONE=$(echo $TRANSMISSION_GET_REMOTE_TORRENT_HASH | grep -o -P '(?<=Percent Done: ).*(?= ETA)')
        PERCENT_DONE=${PERCENT_DONE%\%}

        if (( $(echo "$PERCENT_DONE < 100" |bc -l) )); then
            announce_list=`wget --no-check-certificate -qO - ${base_url}/$TR_TORRENT_HASH | grep -Eo "${pattern}"`

            if [ -z "$announce_list" ] ; then
                echo "No additional trackers found for $TORRENT_ID $TR_TORRENT_HASH $announce_list"
            else
                for tracker in $(wget -qO - ${base_url}/${announce_list}) ; do
                  echo "Adding ${tracker} to $TORRENT_ID $TR_TORRENT_HASH"
                  /usr/bin/transmission-remote REPLACE_WITH_YOUR_TRANSMISSION_URL --netrc /home/REPLACE_WITH_YOUR_HOME/.netrc --ssl -t $TR_TORRENT_HASH -td ${tracker}
                done
            fi
        fi
    fi
done

Nice. But there is actually an easier way although it was tough the information was hard to find :
But first you need the CLI version of Transmission. If you are on Ubuntu, you get it with sudo apt-get transmission-cli

There's actually an example in the man page on how to replace your passkey/passcode in the torrents tracker urls:
transmission-edit -r old-passcode new-passcode ~/.config/transmission/torrents/*\.torrent