There is no such API. You could write a database script or a standalone application that does the job for you. Note that you don’t need to change the namespace prefix of every
activiti attribute but only the namespace url of the
activiti namespace to
http://camunda.org/schema/1.0/bpmn, assuming you only use extension attributes that exist in Camunda as well. In general, make sure to back up the database contents before doing this as you can easily break your process models.