Why can't you edit domains if they are used in a foreign key constraint? What kind of nonsense is that?

If you have a natural key that is used in many places and the datatype ever or rule ever change (and they do in real business systems), you have to manually drop/recreate every constraint that refers to the domain in Firebird. How can Firebird call itself a relational DBMS when it fails to support domains properly?!?!?!?!?