How to upgrade 1511 from Home to Pro?

So are you saying the following will not work ?

Install Win7 Pro or Win7 Pro SP1

 (SP1 is necessary if using the GWX app in Win7, but not if using the 1511 Media Creation Tool created media)

Upgrade to Win10 using the 1511 Media Creation Tool media or the Win7 GWX option

 - Note, Unlike the MCT created media, the GWX route has pre-requisite Win7 KB's that should be installed prior to upgrading to 10

After upgrading to Win10 and verifying it was activated as Win10 Home

 -  use the Change Product Key function and enter the Generic Win10 Pro product key to convert it to a non-Activated Win10 Pro

Use the Change Product key function(or the slui 4 method Greg C. provided) and enter your Win7 Pro product key and wait for it activate Win10 Pro and assign the device a digital license.

Once activated and logged on to Windows with a MSFT account(previously used and required for Insider build) join the Insider Program.

Ok, so here's how it shakes out.  I wiped my SSD, removed all partitions, and did a minimal clean install of W7 Pro.  Then I upgraded to W10 Home (since that's all there is for us to work with now) via GWX, again without updates and keeping nothing. When that was installed I had a nice bleak desktop, missing some icons from the task bar (e.g. Store, Edge, Explorer).  I went to U&S and opted back into Insider Previews.  After restart to upgrade back into the program, I used an ISO of build 14251 and was back to technical preview mode, albeit now for Home.  I have an ISO for build 14279, but was unable to install it because, despite the supposed death of serial keys, it prompts you to enter one.  So that's it.  I only wasted 6 months testing Pro on this machine. I don't mind the year wasted on my wife's HP, because she wants 8.1 back on it,   Since it dead ended into this very build of Home 3 builds ago, without getting an Update to 14261, 14271, or 14279, I don't expect too much going forward.  This has been the most poorly executed beta test I have participated in over the last 30 years.  Yet I will continue with my other four testbeds, and hope nothing bricks them, because there is no support for us.  L1 support merely points us back to ourselves, and we have no one but each other.  Feedback is pointless since issues still exist that were here as far back as build 9926.  Many threads have devolved into circular conversations, and infighting among Insiders  We have become a rudderless ship on a rocky ocean.

Ok so I've done every single one of the above.  I've tried all the workarounds.  It would seem that either the statement from the Devleopment team claiming version parity upgrades when recovering from failure, was either not realistic or an outright lie.  So I'm left with 2 choices, reinstall 7 because reversion has caused my W 7 Pro key to be invalidated upon completion, or use the ISO I have from MCT to reinstall Home, then catch myself up eventually on the Fast Ring.  I refuse to buy a bloody key to test any software.  Every software company on the planet but Microsoft seems to understand this.  I'm testing too many other titles to keep playing ring around the rosy with this.  The true fix for this is for me just to go back to Linux on this machine.  I thank all of you who tried so hard to help me, but your hands were tied and you never knew it.  Good luck with this mess.  

Michael

I did the in place upgrade this time. I'll give the proceedures you posted again. The slui 04 cmd has burned me twice tho.  when I talked to our awesome outsourced L1 support, they said that the pro that was in place after converting via the generic pro key was a retail copy.

I'd like to see the steps too, including....

Original qualifying Win7 edition in place on the device (Home or Pro)

 - activated or not activated (the former is necessary to upgrade, the qualifying o/s has to be seen as genuine by the installer)

Method the upgrade to Win10 was performed

a. Using the 'Download Tool Now' option(Media Creation Tool) on the Windows 10 web page

 https://www.microsoft.com/en-us/software-download/windows10

 which provides a Run or Save as using this 17.5Mb file

==>'MediaCreationTool.exe'

and provides the ability to create Windows10 1511  media(USB or DVD) or an ISO file for mounting

or

b. Using the 'Upgrade Now' option on that same Windows 10 web page

 https://www.microsoft.com/en-us/software-download/windows10

  which provide a Run or Save As using this 7.3 Mb file

=> 'GetWindows10-sds_____________.exe'

I did the in place upgrade this time. I'll give the proceedures you posted again. The slui 04 cmd has burned me twice tho.  when I talked to our awesome outsourced L1 support, they said that the pro that was in place after converting via the generic pro key was a retail copy.