Changing selection marquee

After selecting a picture in the standalone viewer the mouse pointer turns into a hand, but there is no way to move or resize the selection marquee. Or is there?

(This has been asked before, I just didn't want to revive the old thread.)

Background: I am trying to speed up my picture cropping. gets the job done, but an all-Opus process would definitely be faster.

Currently, there's no way to resize a selection rectangle in the image viewer other than making a new selection.