Mabzza

Not sure if it is any use to you now, but I was successful in using a filter for the category slug change.

// Change Category Slug
function change_category_slug ( $args ) {
  $args['rewrite']['slug'] = _x( 'unique_category_name_here', 'Reset Your Permalinks After', 'job_manager' );

  return $args;
}

add_filter( 'register_taxonomy_job_listing_category_args', 'change_category_slug' );

There is good documentation and customisation examples on the plugins website. Hope this helps!