> Late to the party, as usual...
I would have put the "Up/Down" buttons in the gutter between the two boxen, above or below the "Left/Right" arrows. Enable them only when a "Selected" library is selected and movable (not at the top/bottom and, I presume not a locked library).
While it's not likely, if I add a library to the end of a longish list, but need it to be a higher priority, I just <s>fully qualify all calls in code</s> would simply select it in the left box, add it to the right bo