How to alter the result of my view using filters?
you should use hook_views_query_alter, because hook_views_pre_render is called after the query is done, so you cannot influence your database request anymore.

The views documentation has been added to the Drupal api docs recently, so for more info look at:
http://api.drupal.org/api/views/docs%21views.api.php/group/views_hooks/7

or

http://views.doc.logrus.com/