Laravel - Is it possible to modify the collection in eager loading constraint?

I'm trying to modify this query:

The function of the helper class returns me the products left by removing the amounts used in sales, etc. It works fine if I use dd() inside the function. However, the $products collection isn't changed, what am I missing to successfully modify the base $products array with the collection returned by the helper?

If it helps, here is the helper class:

If there is a better way to handle this, I am glad for every suggestion.

Best regards

via Chebli Mohamed