Isn't drag and drop working for you? I think you can reorder requirements by dragging them and making sure you do not drop them as a child of something else. I can double check that today but i do think that works.
Your requiremtns are numbered in sequential order, and can not be moved to other locations in the heirarchy. It would require you to renumber your requirements on the backend and this is a dangerous excercise to say the least.
"This may hurt a little, but it's something you'll get used to."