Suspend replication at the master def site ...
BEGIN
DBMS_DEFER_SYS.SET_DISABLED ('masterdef_name',TRUE);
END;
/
commit;

DDL will get replicated ...

BEGIN
DBMS_REPCAT.EXECUTE_DDL (
GNAME => 'CODES',
MASTER_LIST => 'masterdef_site,other_mastersite',
DDL_TEXT => 'alter table mis.QUALITY ADD (
SHOW_IN_INVY CHAR(1),
GOOD_PROD_FOR_SHOP CHAR(1),
TRANSFER CHAR(1),
ALLOW_WASTING CHAR(1))');
END;
/