- run CMD as an Administrator

bcdedit -set loadoptions DISABLE_INTEGRITY_CHECKS
bcdedit -set TESTSIGNING ON

- Reboot

- Right click on Intel CT desktop adapter in device manager, update driver
- Browse my computer for driver software
- Select driver from list
- Have disk
- Point to folder PRO1000\Winx64\NDIS63\
- Select Intel Gigabit CT Desktop Adapter (unsigned - with excamation mark)
- When asked if really instal unsigned driver, confirm
- Run APPS\PROSETDX\Winx64\DxSetup.exe (if you cannot install make one more reboot)

- run CMD as an Administrator

bcdedit -set loadoptions ENABLE_INTEGRITY_CHECKS
bcdedit -set TESTSIGNING OFF

- Reboot

Voila! Now you have Win8.1 with original Intel driver.

p.s.: it's Intel 19.1 driver, the only "patch" are next 3 lines added to file \PRO1000\Winx64\NDIS63\e1q63x64.inf

[Intel.NTamd64.6.3]
%E10D3NC.DeviceDesc%            = E10D3,               PCI\VEN_8086&DEV_10D3
%EA01FNC.DeviceDesc%            = E10D3,               PCI\VEN_8086&DEV_10D3&SUBSYS_A01F8086