I am still not sure I understand what you're trying to do. You're implementing the bureaucracy_handler_interface
interface, which makes me think your'e using the "script mode" action.
Further up you mention storing something in struct? Struct data is only handled in "template mode" when saving a page that has the appropriate schema assigned.
Are you trying to modify field values in your script before they are passed on in template mode?
That's not how script mode is supposed to work. Script mode is meant to handle the data on your own, not to modify it and have it pass on to other modes.
In theory it might be possible to handle the fields and store the data in struct yourself...
But again, I don't really understand what you're actually trying to accomplish.
juergen-aus-zuendorf I am looking for a way to assign a GUID value to a struct parameter (struct plugin) via PHP script
Wouldn't it be more sensible to implement this as a new struct field? Why the bureaucracy involvement?