Expanded Order Management POST API

The Order Management GET API is very thorough and you can get a lot of information about orders, the products in them, and the customer who placed them. In comparison, the POST API is very limited, only really allowing you to change the status of items to produced or shipped.

Ideally we would like to have the ability to add orders, rather than just change existing ones through the Order Management API. If this is not possible, we should at least have the ability to modify sizes/colours, maybe splitting an order line into multiple if say, there are 5 black shirts and we want 3 of them to be red. We should also have the ability to change any custom fields that have been added to the products.