Assign a category by user and customize the edit-tags.php?taxonomy=category page

This is how I did it :

function if_restrict_categories($categories) {
  global $current_user;
  $a = get_cat_if_user($current_user->ID);
  $onPostPage = (strpos($_SERVER['PHP_SELF'], 'edit-tags.php'));

  if (is_admin() && $onPostPage && !current_user_can('level_10')) {
  $size = count($categories);
  for ($i = 0; $i < $size; $i++) {
      if($categories[$i]->parent != $a && $categories[$i]->term_id != $a){
     unset($categories[$i]);
      }         
  }
   }

   return $categories;
}
add_filter('get_terms', 'if_restrict_categories');

And where get_cat_if_user() is a custom function where I get the category I’ve assigned to my user.

Hopes it helps others.
Cheers.