Some countries, as Kosovo, there is no IBAN generator available.
In these cases, SAP acts in accordance with the recommendations of document bellow. For Kosovo, see page 45.
http://www.swift.com/dsp/resources/documents/IBAN_Registry.pdf
The custom settings should be maintained in transaction OY17.
In additional, for more information and how to create their own IBAN generator, customers can see note 1447813, point 1 "Country-independent settings".