Windows 10 in various scenarios will turn windows update back if all you do is disable the service.
Easiest way I found to disable updates in Windows 10 is to goto the Windows update Service property window, disable it, then goto the Log On tab at the top and click This account: and type ".\Guest"(no quotes), clear the password fields and click apply.
You will get a message saying Guest has been enabled to do this, but the hitch is that "Guest" doesn't have permission to do it so Windows update is basically disabled no matter what unless you switch it back which is just as easy.