The best tool for bulk reorganization is the Library window. Either:

• "Show All Bookmarks" from one of the short bookmark menus
• Ctrl+Shift+b

You'll find a folder tree in the left column. Selecting the name of a folder there will show its contents on the right side.

In the list on the right, you can use the typical multi-select feature for Windows:

• To select a contiguous range, left-click the first item and Shift+click the last item
• To select multiple individual bookmarks, hold the Ctrl key while clicking to add or remove an item from the group

Does that work for you?

I should mention, just in case, to undo the last action, either:

• Organize menu > Undo
• Ctrl+z