If I now turn off the Insider program on that machine will it then act and receice updates as a machine that has never been in the Insider program.
Leaving the Insider Program (now) does not seem to be easy to do. Looking at your question I decided to try it.
First you get some options
My choice basically kicked me to the Reset page. I figured.... what the heck and went ahead with the reset, since I didn't have many programs or apps installed to lose.
Afterwards, I found my machine still on 15063 and ran Windows Update manually and got the Cumulative Update which bumped me to 15063.11
Hardly worth the hassle, and.....
I'm not absolutely sure that I was ever completely off the Insider Program.
After the reset completed and I was back to square one with all my Tiles and desktop icons set to defaults, I checked and while it was greyed out it showed some text that said something about
"Your machine is configured to receive Insider builds" and the box underneath had reverted from "Fast" to "Release Preview" and it was also greyed out.
Then after installing the Cumulative Update, which required a reboot, I went back and then it had a message "Fix Me" which referenced some changes that it need to apply to some security settings somewhere.
After which I got this
Clicked "Confirm" which again required a reboot and BOOM back to fast ring.
Big P.I.T.A. to end up back where I started, but.....
I thought I would give it a try anyway.
As I noted in the first image. Might be better to choose the other option and then wait for the actual release to come and go and see what happens.
As a side NOTE.... My production machine, which is not nor has it ever been an insider machine, that I manually upgraded to 15063.0 using the published official Msft ISO did get the same cumulative update and is now at 15063.11
Not sure if any of this helps to answer your question or not but it kept me entertained for a few hours.