You want to derive fields like transportation zone and country based on the business partner...

Use the access class to derive the fields based on the Business Partner Group field in the user interface when the change request is submitted.

Use a custom feeder class to derive the fields based on Business Partner group field in the user interface.

Use the CROSS_ENTITY_BADI to derive the fields based on the Business Partner Group field in the user interface.

Use Business Rule Framework Plus (BRFplus) to derive the fields using a decision table based on the Business Partner Group field in the user interface.