If you try to use a generic product key (e.g., for Pro) but the media is locked to Core, you’ll get an error during installation. Deleting or editing ei.cfg resolves it — provided the key matches an edition actually in the image.
To make your Windows 8.1 installer behave like a flexible, edition-choosing menu (without requiring a product key during installation), your ei.cfg file must contain the following three lines: ei.cfg windows 8.1
Even after you bypass the initial product key screen, Windows 8.1 Setup will eventually ask for a key before the installation completes. You can use Microsoft's official (also called "default keys") to proceed. These keys allow installation but cannot activate Windows. If you try to use a generic product key (e