Update custom field in CiviCase using batch profile?
There is a write up here about using the API. May not be a lot of help to you but worth adding to the thread. I found it, and your question, while similarly searching for a solution to needing to 'bulk update' Cases - and having found and failed (in our situation) with VBO and Views it may be a case, for us at least, that we need to do some more development with VBO and civicrm Entities