As long as the tree is dormant you are fine doing it now. Doesn't have to be below freezing. I just moved a tree last weekend. One thing that I would recommend is watering the tree after the transplant, even in the fall when it is cold. This is not so much for the tree but to compact the soil around the root ball to remove air pockets. Air pockets = dead roots. If you do move it this fall just remember to prune the top back a bit late winter to restore the crown to root balance, as for sure you will have some root damage in the process.