Q:

Magento 2 API: Possible to edit an order? 

I would like to know whether it is possible to edit an order via API analog to the functionality in the Magento 2 backend. 

A:

Out of the box it's not possible as you can see from this file: https://github.com/magento/magento2/blob/develop/app/code/Magento/Sales/etc/webapi.xml
The only modifications you can do to an order via API are:

cancel
send the email 
hold
unhold
comment
create (which is not really an edition)

