Some members have confirmed that running the main installer once more has proved the ability to do this. However, we use versions of rTorrent and libtorrent that are globally supported and therefore I hardly see reasoning to downgrading the two. If you would like to update Deluge there is currently a command for that, just type
upgradeDeluge as root to begin the update.
Although, if you think this is something (Downgrading) that you would like to see implemented into the QuickBox toolset, feel free to open a Feature Request and we'll discuss the possibilities as well as see if other users would be interested in such an option.