I know it is probably covered elsewhere, but how do I add a tracker URL to a list of trackers for a running torrent?

Thanks, I found it while trying to do something else. Problem Solved !!

If you are using the same set of trackers for all your torrents, you can add them in the setings

Settings
Transfers
Option 2

I have a set of trackers that I use and once added, any new torrents, will automatically be added.

You can even remove pesky trackers that you DON'T want under option 1