If you want to remove a cal from a user, you can use the QMS API in QlikView to deallocate the cal. Keep in mind that deallocating the cal does not make it automatically available again. There is a 24 hour quarantine with QlikView 11.2 and a 7 day quarantine with QlikView 12 before the cal is allowed to be reallocated.
Definitely, do not attempt to modify pgo files.
To my knowledge there is no sample code for performing this activity. Here is the link to the QMS API: QlikView Management API - Getting Started and Examples