A few days ago I added some batch update features to the web interface. From most lists, you can now use the checkboxes along the left side to select multiple items, then you can use the Batch Update and Batch Delete boxes in the left column to modify or delete the selected items.
For example, you can select multiple songs and then add or remove a tag to all of them, or set their color, or set the value of a custom field. Or you can select multiple transactions and change their category if you want to reorganize your past transactions. Or you can select any unconfirmed events and delete them from your account.
Of course, these changes will then appear on your mobile devices the next time you launch the BandHelper app there.