For Windows 10 users, you can do this:
i) Press Windows Key + X to open Power User Menu. Select Command Prompt (Admin) from the menu.
ii) Once the Command Prompt open, enter bcdedit.exe -set loadoptions DISABLE_INTEGRITY_CHECKS and press Enter. Then enter bcdedit.exe -set TESTSIGNING ON and press Enter.
iii) Close Command Prompt and restart your PC.
If this fails for some reason, you can reboot with Signature checks disabled by rebooting into advanced options (Hold left shift key while hitting reboot button) and hit F7.
You need to copy the modified atikmdag.sys file into your drivers folder as well (C:/Windows/System32/Drivers)
File can be found here:
HereI have just bought one reference RX480, flashed mod bios, with stock driver I get Error 43 in device manager.
If I replace atikmdag.sys with the modified one, I get Error 31 in device manager.
"bcdedit.exe -set loadoptions DISABLE_INTEGRITY_CHECKS" and "bcdedit.exe -set TESTSIGNING" are done, both windows installations are in testing mode.
Tried both Win7 and Win10, original drivers 16.7.3 and 16.8.2, result is the same.