It is not possible to allow an approver to edit an order or an e-Doc Product and then save it to allow the original customer to review the edited file before placing the order. The approval plan will only trigger once the order is placed.
As an alternative you can allow the approver to impersonate as a user on site and allow “save for later” on the site. Once you allow the users to impersonate the site users on the site, the original user can customize the template and then save it for later and inform the approver about the item in save for later. The approver then can impersonate as the original user and go to saved for later and check and edit the customized product and save it again.
The original user can then review the changes and complete the order.
If you keep the approval plan active on the site, the approver will be able to see the final file that the user has ordered and may approve or deny based on the final changes made by the original user