Stripping OIDs from tables in preparation for pg_upgrade
That UPDATE might work, but I am not certain, and I wouldn't want to do that with data I value.  You don't have the option anyway, since you cannot get superuser access in a hosted database.
I can think of a safe, but more painful method:

Briefly suspend data modification activity on the table.

Create a trigger that records all data modification activity in another table.

Create a new table that looks like the old one, and start an INSERT INTO ... SELECT ... that copies the data.


Now normal operation can be resumed.
Once the copy is done, replay the recorded changes. Then

Start a transaction.

LOCK the original table.

Replay all the changes that happened since the last replay (should be few).

DROP the original table.

Rename the copy to the original table name.


Foreign keys will require extra attention.