Last time I did that, I copied all the .torrent files I downloaded (I always keep them) before and load them into the client again (azureus in my case). After that I had to tell the client where the files for the torrents were, since the path was different.
No need to make new torrent files, since the tracker won't know them. If you do not have the original torrent files you can either download them again from the tracker or I think you can export them from the client (I think...)
I hope this helps a bit in your quest...
