How to change customs document via /sapsll/api_6800_synch

Dear experts,

Scenario & Requirement:
We don't have SAP ERP as the feeder for customs document, and we have a option to create the customs document manually. Afterwards we need to change the manually created customs documents. The actions for creation and change are triggered from the Fiori app, as the backend side we try to use FM /sapsll/api_6800_synch for implementation.
For the change scenario, we may change the quantity/amount of an item, and we want the system to trigger rechecking license assignment.

Open question:
There's so many non-optional parameters need to be supplied for /sapsll/api_6800_synch. If we just want to update the quantity/amount, can we just leave some mandatory parameters empty and what're the fewest parameters we need to supply?

Appreciate if you have such experience to share!