Two mistakes in the above post:
Originally posted by BV1963
When you import you will have to say ignore = yes, otherwise import will fail since all tables already exist.
You don't have to (and should not have to for the purpose specified) use IGNORE=Y, you should use IGNORE=N. IGNORE=N will not abort the import process when it encounters allready existing object. It will simply report the object creation error in the log file, skip processing that object entirely, and continue the task with the next object. While setting IGNORE=Y will merely ignore the object creation error, but will continue to load data for that object! And I don't think this is desireable when you only want to import PL/SQL objects.

If you say ignore = yes it will not replaced old stored procedires with new ones since they already exist!
That's not true either. Import will simply replace the old procedures with the ones contained in dump file. That's because procedures, packages and other PL/SQL stuf (as well as views) are defined with "CREATE OR REPLACE ...." in the dump file. So Oracle will simply REPLACE old objects, there will be no errors to ignore. With segments (tables, indexes,...) it is different, because there is no "CRATE OR REPLACE TABLE ...." command available in SQL - that's why you have to use IGNORE=Y/N for those objects. But it only aplies to those kind of objects, it has no effect on procedures, functions, packages, triggers, views etc.