The way I understood it, it might be something like this: there's a simple table:

SQL> create table test
  2    (id         number,
  3     name       varchar2(5)
  4    );

Table created.

The upgrade script might then - for example - add a primary key constraint:

SQL> alter table test add constraint pk_test primary key (id);

Table altered.

Then, during work with the table, you'd want to insert a row and hit an error because column is too small:

SQL> insert into test (id, name) values (1, 'Littlefoot');
insert into test (id, name) values (1, 'Littlefoot')
                                       *
ERROR at line 1:
ORA-12899: value too large for column "SCOTT"."TEST"."NAME" (actual: 10,
maximum: 5)

OK; enlarge it:

SQL> alter table test modify name varchar2(20);

Table altered.

SQL> insert into test (id, name) values (1, 'Littlefoot');

1 row created.

SQL>

Therefore, the upgrade script would contain two statements:

alter table test add constraint pk_test primary key (id);
alter table test modify name varchar2(20);