So, after about an all night NTLite-like Scavenger Hunt last night, trying to find the one file that would allow me to keep my files and apps during a refresh my old 1909 with a newer 1909, I finally gave up and I did a Host Refresh using Win10 2004. (Which might have been the better choice in the end, since MS
fixed the Search bar problem in 2004. (Apparently related to MS moving Cortana out from the Search function. (I am finding that Cortana and Search are tied to TimeBroker. Disable TimeBroker and you disable both of them.)) And 2004 has a
Hardware Scheduler which now works with Nvidia GPU's.)
For anyone interested, here are some of the things that I tried:
First, since 2004 allowed me to keep my files during a Refresh of my older 1909, I thought that perhaps I could find (and then hack) the one file (assuming there was only one) that had allowed me to keep my files when I used 2004 to do a Host Refresh.
So I started to copy parts of a 2004 wim over to the folder containing the newer 1909 wim, testing each time (by running setup.exe) to see if any new file would allow me to keep my files during setup.
Interestingly, the file dates for the last (newest) 1909 were 10/7/2020, and the dates for 2004 were 10/8/2020.
Copying the boot folder didn't make a difference. Copying exe's from Source didn't make a difference. I finally found that setupplatform.dll was a critical file.
I was hoping that maybe I could hack that with a hex editor, but I never got around that trying that.
I also thought that perhaps I could find a difference in the xml configure files between the two wim's and hack one of those to work. (Would have been many hours with WinMerge, comparing files.)
I changed plans and tried to find what differences there were between my old 1909 and my new 1909 that allowed the latter to refresh over itself.
So I pulled up regedit from both (a vanilla install of new 1909 running in a VM) and searched for "1909." I found slight differences between them. My old 1909 ended with .488 in the Registry. Whereas my new 1909 had 1139 instead. Plus some other different numbers related to version when I saw them nearby.
So I changed all the build numbers (or whatever they're called) in the Registry of my old 1909 to match the new 1909, hoping that it would look like the newer 1909 and trick new 1909 into letting me keep my files during a Host Refresh.
Surprisingly, that didn't work.
Perhaps I missed one. Or perhaps build numbers are also in hex in the Registry.
Another interesting thing I noticed during all this is that both old 1909, new 1909 and 2004 have an update called "Feature Update to Windows 10 20H2 via Enablement Package" (dated 9/27/2020) in them.