I received a reply from The Game Master himself. Here is where to find the file.
"Yes you are correct, Windows 10 hides it very well, in a different location then where we used to have it. Thanks for pointing this out. I should change the techsupport page on this.
Its in...
C:\Users\WhateverYourUsernameIsInWIn10\AppData\Local\VirtualStore\ProgramFiles (x86)\Avernum 3\Data\Avernum3.dat"
Can a Moderator or admin please post this Sticky this post in the Genefore 1-3, Avernum1-3 (Original), & probably Blades of Avernum & Nethergate (Original) & Exile Games.