Добавьте массив в другой массив в коллекции Laravel
$collection = collect(['product_id' => 1, 'price' => 100]);
$merged = $collection->merge(['price' => 200, 'discount' => false]);
$merged->all();
// ['product_id' => 1, 'price' => 200, 'discount' => false]
Mohamad