Commission Regulation (EC) No 1998/2000 of 21 September 2000 amending Regulation (EC) No 1374/98 laying down detailed rules for the application of the import arrangements and opening tariff quotas for milk and milk products, and Regulation (EC) No 174/1999 laying down special detailed rules for the application of Council Regulation (EEC) No 804/68 as regards export licences and export refunds in the case of milk and milk products