Was he correct in that there is no way to do an 8.1 Pro install other that a clean on, ie. no "repair" type of install?
In Windows 10 since
version 1511 build 10586 (so called November Update) it is possible to upgrade Windows or perform a repair install even when the
Users folder is relocated, not on C: drive. It is now also possible to upgrade from Windows 8.1 to Windows 10 with relocated
Users folder when upgrade media is said version 1511 or later.
Unfortunately this does not mean that repair install is possible in Windows 8.1 with relocated
Users folder. To do a repair install you would first need to sysprep
Users folder back to
C: drive, then run repair install, and finally relocate
Users back to another drive. In your case now however I don't think it would work but you can of course try.
The process of moving
Users folder back to C: is exactly the same than when relocated from C: to another drive, just change the value of
ProfilesDirectory in answer file to
C:\Users (line 6 in example answer file in tutorial step 2.1).
If upgrading to Windows 10 is out of the question then I really recommend a clean, fresh install.
Kari