Is it possible to sort the ordered file download priority manually?
As it is one can only sort-of manipulate it by setting other download priorities before setting them as Ordered, but that's clunky and unintuitive.

I don't fully understand what it is you are trying to do.

If you have your torrents loaded and sorted by status you will first see those downloading and then those queued starting with 1 and ending at n.  

If you want to move a torrent from the bottom to the top of the queue just highlight it and drag it to the desired position.  

If you want to move a block of torrents click the first, hold shift, click another and all the torrents in between will be highlighter.  Once again, drag them to where you want them.  

If you want to move multiple torrents not in a block you can click as many as you want whilst holding control down.  Once again, drag them to where you want.

Does that help?