drupal hook_update_N() If I install all updates from site_name/update.php, and after change the system.schema_version from 7005 to 7003 using (to reinstall updates 7004 and 7005)

UPDATE system SET schema_version = 7003 WHERE name = 'test';
I then try to run site_name/update.php but it not run because the fields that hook_update_N() adds already exists. And I see when access update.php after error that 2 updates exists.  
After I restore system.schema_version to its initially value (7005)


Are the updates 7004 and 7005 now installed or not?
What are you trying to do, and why are you trying to do this? To be honest, it makes no sense. First off, schema numbers should start at 7000 (in Drupal 7), and you should never be resetting them, particularly within hook_update_N(), as you're just going to cause the same code to be run every time the update process is run.