Changing column type from oid to int4

Did somebody ever try to change the type to a compatible type? I plan to
change a column from oid to int (once it holded a lob, now some sort of id)
with modifying pg_attribute:

update pg_attribute
     set atttypid=(select oid from pg_type where typname='int4')
 where attname='whatever'
   and attrelid=(select oid from pg_class where relname='a_table_name');

It seems to work fine, but I was not sure so I rolled back the change.

So, has anyone ever tried this?

Regards,
 Mario Weilguni