remove tablespace for primary key (*not* by drop/recreate constraint)

Hello list,

Due to there are lots of foreign key dependencies, would prefer not to 
drop/create for primary key. Is there other way(s) for psql8.3 to remove 
tablespace for primary key please?

For example, z1 (c1 text) with pk_z1 PRIMARY KEY (c1), tablespace "abc"

May I know how to remove tablespace(set tablespace to empty for z1)?

Thanks a lot!