Re: can a user edit their order?

That's not possible. Orders are not editable by the user once placed.
You could have a form somewhere where users could ask to have their information updated using a joomla form component. That would mean some manual work for you though.
Otherwise, it would require the development of such feature in HikaShop.

Hi,

There is no way for the customers to edit their order.
That could cause many issues. For example, if the custom item field values would be tied to the price of the product, or if the coupon would change the total amount, this might lead to the shipping method selected during the checkout not being valid anymore, taxes to be recalculated, etc. It's basically a can of worms to allow for that.

What we did however since then is that you can provide your customers with a way to contact you easily from their order.
So if you provide access to the order history, via a menu item of the type "HikaShop order listing" or "HikaShop user control panel" or via the link in the email notifications, users can see a "contact us about your order" button. When they click on it, they get a contact form, where they can enter information. There, you can display extra fields by creating custom fields of the table "contact" via the menu Display>Custom fields. You'll then receive an email when the user validates the contact form.
You can control whether to display the button or not based on the status of the order by toggling the order statuses under the "contact button" column of the System>Order statuses menu in HikaShop.
That way, you can control the information they provide you, and manually modify the order for them in the backend.