Feature update to Windows 10, version 1709 fails to install

You are right to be cautious, beerus_king. But I can't keep saying the same thing over & over. If you can't manage to get to the Recovery Environment of external media & test it out from what I've already written thrice at least - well, you already asked whether a shop could do it. Yes, they can. You should ensure you have made a backup of all important personal files onto external media before giving the computer to them, though.

But I've decided to do a BCDBoot of my own, & will post the results later tonight, if I survive.

I have made a bootable USB drive w10 1709 version.

Dont get me wrong, but when I read your instructions, im actually scared to do it.  I mean, what if something goes wrong. I'm not a "genius" like you when it comes to PC. I dont know what to do afterwards

1. Anyway, I am confused on 

                                        DIR  C:\BU  /a

                                        Also type:  BCDEdit

How do I write the command? like this

                                                         DIR  C:\BU  /a     (do I press enter?)

                            (then enter this?)  BCDEdit

2. what happens

(g) Close the Command Prompt, & click "Continue" to return.

after continue? will my PC boot?

 (legs are shaking lol)

(1) I find "the moment I changed the boot order" to be unclear. Was that after you changed it in this thread to be the Windows Boot Manager (bootmgr)? This was your picture afterward...

Or was it before that? And it's gone now? Anyway, we'll try to get the ability back, if it has gone.

(2) I can't say it much better than I did before...

You already made the backup BCD:  "C:\BU\BCD Backup". Now...

(a) Plug in a Recovery USB drive or a Win 10 Installation media.

You couldn't make a Recovery USB drive. Were you able to make a Recovery DVD (Repair Disc)? If so, you may insert that. I'll repeat how to make that below.

(b) Reboot, & hold the Esc key as it boots just before or after the ASUS ROG Logo shows up..

     The UEFI boot option screen should appear.

(c) Choose the option that boots the USB media or the DVD media.

(d) If it's to the Installation USB, choose "Repair this computer"(instead of to install).

     The computer will reboot to the recovery environment.

(e) At the "Choose an option" screen, click "Troubleshoot > Advanced Options > Command Prompt".

(f) At the Command Prompt, type:   DIR  C:\BU  /a

                                        Also type:  BCDEdit

Do you see "BCD Backup" listed? If not, try letter D:, in case they have switched. Sometimes, the drive letters are different in the recovery environment. Which letter showed the file? Did you get output for BCDEdit, (just to prove it is there)?

(g) Close the Command Prompt, & click "Continue" to return.

If you don't do that - it will be on your head if you can't get there, if it should become necessary.

If/when necessary, to recover the backup BCD, you would enter:

BCDEdit  /Import  "C:\BU\BCD Backup"

Here is how to make a Recover DVD...

Try to make a Recovery DVD (Repair Disc), at "START, Settings, Update & Security, Backup, Go to Backup & Restore (Win 7)" (or ask Cortana for Control Panel, & select Backup & Restore)...

3.  Yes, i was able to boot on d drive. It was the moment i change the boot order. 

4. I dont know how to do that."recovery environment"

Thanks for doing this.

I've got to hit the sack & will resume tomorrow. I haven't as yet found a truly bad experience with it. Here is a bigger explanation on what BCDBoot does...

https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/bcdboot-command-line-options-techref-di

BCDBoot Command Line Options

(1) I puzzled a bit over what it says about the "/s" option, but still think we should use it because of possible confusion with the system partition on your D:drive.

(2) I'm unsure whether you end up in a dual boot with the Windows on D:drive. We should be able to remove it afterwards, if unwanted.

(3) You never answered:  Were you able to boot to Windows on the D:drive?

(4) Have you tested that you can get to the recovery environment?