(BTW, is there any way to delete the update service entirely?)
From what I've found in previous research, no. I'm sure there is a way, but it'll likely take hours to figure out, and I don't exactly have Windows 10 at my disposal here at work. It looks like there may be some ways to disable it if you're using Windows 10 Professional or higher. But beyond that, it looks like you might be looking at isolating the updating software on your own, and either removing the files manually and any pointers to them in the Registry, or deleting any trace of them using a separately booted OS to bypass embedded Windows Security measures that might run at boot time or with the OS.
Since they were so dedicated to the idea of maintaining forced Updates at all times, I suspect the Automatic update software is broken into multiple system files/processes that are connected to other necessary System Apps, or it is simply embedded in a specific, necessary system file/process. I also suspect that in order to remove the Automatic Updates permanently, you would need to 1.) Circumvent OS File checks at startup so that you can 2.) Patch the file(s) the update software is embedded into (like maybe inserting a simple JUMP over the update code).
I've got a computer that can run Windows 10, and I did consider taking a look at it for the sole purpose of removing the update software permanently. If/when I do end up installing Windows 10 on it, I'll let you know what I find. Unless of course you find a way to remove it first. I feel like someone's been able to remove it by now.
I'm sure you could find something if you Googled long enough. Because when it comes to application security, it's almost never about "Can we break it?" It's about "When will it be broken?"
EDIT:
It appears that they've found a few workarounds after a quick Google Search.