CREATE TABLE transactions
  ( id NUMBER
    , transaction_date DATE
    , value NUMBER)
  PARTITION BY RANGE (transaction_date)
  INTERVAL (NUMTODSINTERVAL(1,'DAY'))
  ( 
   PARTITION p_before_2007 VALUES LESS THAN 
     (TO_DATE('01-JAN-2007','dd-MON-yyyy'))
  );

  ALTER TABLE transactions 
    SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH');

ORA-14767: Cannot specify this interval with existing high bounds

SQL> CREATE TABLE transactions
  2    ( id NUMBER
  3      , transaction_date DATE
  4      , value NUMBER)
  5    PARTITION BY RANGE (transaction_date)
  6    INTERVAL (NUMTODSINTERVAL(1,'DAY'))
  7    ( 
  8     PARTITION p_before_2007 VALUES LESS THAN 
  9       (TO_DATE('01-JAN-2007','dd-MON-yyyy'))
 10    );

Table created.

SQL> ALTER TABLE transactions 
  2      SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH');
    SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH')
                                           *
ERROR at line 2:
ORA-00907: missing right parenthesis


SQL> ALTER TABLE transactions SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH'));

Table altered.

SQL> @v

Version Oracle : 11.2.0.1.0