Which is the correct procedure to add new columns to a table with one or more FKs

When I add a column on a table that has the foreign key constraint with istruction

ALTER TABLE REGOLA_ELISIONE ADD (FLAG_PERIODICO SMALLINT DEFAULT 0);

I get the following error: 

“Could not execute 'ALTER TABLE REGOLA_ELISIONE4 ADD (FLAG_PERIODICO SMALLINT DEFAULT 0)' in 49 ms 502 µs .

SAP DBTech JDBC: [7]: feature not supported: cannot add column of referencing row table”

If I delete a foreign key from a table, add a new column and then I try to ecreate the FK just deleted, I get the following error 

“Could not execute 'ALTER TABLE DATI_CAUSALI ADD CONSTRAINT FK_DATI_CAUSALI_002 FOREIGN KEY (COD_ELISIONE) REFERENCES ...' in 49 ms 516 µs .

SAP DBTech JDBC: [7]: feature not supported: cannot create foreign key constraint on referenced table having added column”

  Could you please help us with Issue? Which is the correct procedure to add new columns to a table with one or more FKs?

Thanks Paola