Retrospective fix to hook_update_n() in current release
You can reset the status of the hook_update_n from below query
update system set schema_version=0 where name='modulename(hook)';

Then you can run update.php so this hook_update_n() will work again with your latest changes.

Also you can see this link for schema_version values system_schema() why we have to set schema_version '0' instead of '-1'.

you can use following drush module for roll back the update version in the system table. Called "uroll" for update rollback.

https://github.com/danshumaker/drush-uroll

Usage: drush uroll --module=mycustommodule --version=5

This combined with a database backup reload script allows you to rinse and repeat when writing update functions