Hi Erk
It is not possible to maintain STCEG from this FM.
Due to SAP customers' requirement, note 361364 was created to offer the functionality of adding tax/vat nmbers to one-time cusotmers. The cusotmer requirmeents consisted in being able to matinain these tax/vat numbers when using dialog transaciton, let's say VA01 or VA02.
But As stated in note 361364, it is not possible to maintain these fields using BAPIS.
You will need to modify the system to achieve the requirement.
I am sorry to say this, but it is the current situation.
Best regards,
Hualin