Bulk move content from one category to another - Drupal 7
Have you checked out Views Bulk Operations? How to batch assign taxonomy terms to nodes using Views Bulk Operations is a good blog post about how to accomplish this. Basically, make a view that displays the nodes you want to edit. Add a VBO field to this view (using the instructions in the above blog post) and then go to the page you created with the View to do bulk operations on the desired nodes.