I was just asked to update tax classes on products in the catalogue. I found a easy and fast solution.

Connect to your database and find the table called: yourStorePrefix_eav_attribute and find row containing name of attribute: tax_class_id (this may differ in some versions/installations of magento!) – mine had ID: 81

Now we have to find out what value is assigned to the prefered tax class, which we want assign to all products. You can find it out in the table called: yourStorePrefix_tax_class. Mine was: 2

Than go to you sql query editor and run the following command:

UPDATE yourStorePrefix_catalog_product_entity_int SET value=2 WHERE attribute_id=81

P.S.: Do not forget to renew all cache and rebuild all catalogue indexes – otherwise this change will not work on frontend!

That`s all folks!