Bulk Update allows you to update several tasks at the same time. Use the "Search" function to narrow down the list down to the tasks you want to update, and then use the "Not this" links to remove tasks you weren't able to sort out of your list using "Search." You can now change the due date, the tags, the priority or any other task detail on all of those tasks all at once.
You can use Bulk Update to, for example, change the tag "money" to "spending":