add_filter('product_cat_rewrite_rules','update_base_category_rewrite_rule');
function update_base_category_rewrite_rule($category_rewrite){
    $new_category_rewrite = $category_rewrite;
    foreach($category_rewrite as $key => $value){
            $xyz = str_replace('foo', 'products', $key);
            $new_category_rewrite[$xyz] = $value;
    }
    return $new_category_rewrite;