Reassigning surrogate keys?

I have a few tables with surrogate keys (SERIAL PRIMARY KEYs unique to each tables). These tables are used by other tables, with references to these keys. My usage of these is quite simple :

select * from table_a; oid | data-----+------  1  |  foo  2  |  barselect * from table_c; a_id | b_id |   misc------+------+----------  1   |   1  | whatever  2   |   1  | blah

There are no SQL constraints or whatever.

I'm about to make some large modifications to my DB (e.g. addition and merging of tables), so I'm wondering if there is an easy or automatic way to reassign OIDs in related tables ?[Edit : I guess there is no reason such an automatic way should exist, since those keys are assigned manually and not by the DB itself.]

I don't like the idea of having "holes" in my surrogate keys so I'm thinking about "leveling" them (probably using temporary tables with corresponding new/old keys), but is it worth the trouble ?

I'm using PostgreSQL 9.3.5.