There are several instructions available on this site for changing an MBR to a GPT format. I previously shared a method using a Win10 utility.
I'm not suggesting it's impossible, your guide sounds excellent. What confuses me is the reluctance to perform clean installations. With cloud profiles and importable/exportable settings everywhere, it feels like a hassle. After a quick clean install, I can be back up in just 20 minutes—almost as if nothing happened. It seems so simple whenever a new graphics driver is released. Perhaps slower internet would make the process feel more daunting though.
It's frustrating when it feels like a long time to get everything back up and running after reinstalling apps, drivers, and setting them up again. I'm surprised how quickly a fresh install can finish in just 15 minutes, but it still doesn't account for the OOBE.