call to drupal_alter does not allow alter of $context

In order to allow multiple votes on the same content for a single user (https://drupal.org/node/1006630) we are using hook_rate_vote_alter to set $context['criteria'] = array();

This revealed that hook_rate_vote_alter is actually not able to change anything in $context; see https://api.drupal.org/api/drupal/includes!common.inc/function/drupal_al... -- specifically the part about $data['__drupal_alter_by_ref']