Add existing custom option to cart item if the option was not included initially

Question

I can update existing cart values:

$item = $quote->getItemById($itemId);
$item->getOptionByCode('option_code')->setValue($value);
$item->saveItemOptions();

But this only works if the option already exists, e.g. an unchecked checkmark custom option will not be included in the item options when adding the product to cart. I tried adding the options with $item->addOption() but that doesn't work because the option is not included in the $item->getProduct()->getCustomOptions(), and trying to add the custom option there also modifies the actual product instead of just the cart item product.

Is there a way to add an existing custom option to an existing cart item without removing and re-adding the item?

Answer 1

Spent 2 days trying to figure this out and of course I find the answer an hour after asking a question:

        $buyRequest = $this->serializer->unserialize($item->getOptionByCode('info_buyRequest')->getValue());
        $buyRequest['options'][$code] = $value;
        $item->getOptionByCode('info_buyRequest')->setValue($this->serializer->serialize($buyRequest));
        $item->saveItemOptions();
        $quote->updateItem($itemId, $buyRequest);
        $this->quoteRepository->save($quote);

Using the $quote->updateItem() method with an updated info_buyRequest pushes the update to the cart product as well.