You want the system to consider your authorization to maintain and display only certain business partner master records in the dialog with the F4 helps for the business partner as well.
Therefore, you only want to be provided master records in the selection list when you are searching a certain business partner which you may process according to your maintained authorizations.
You want this function to be available with F4 helps for the business partner field as well as with the locator search help in the business partner maintenance (Transaction BP) and in the search for business partners in the CIC (here via BAPI BAPI_BUPA_SEARCH).