Disabling drivers signature enforcement

Hello. I've had to partially reinstal my Win8. This means I lost almost all my software and drivers. Now I have the headache again. On previous OS instance I had somehow disabled strict drivers signature (WHQL) control, so I was able to install even unsigned drivers like betas. Now on new OS, the annoying messages popup again and I can't for god remind where I had it disabled.
What I have:
- uninstalled defender
- disabled UAC by sliding the slider down (however UAC is still reported as active in Security Center - a guide to totally get rid of UAC would come useful )
- This hack doesnot remove the problem.
I know for sure this control can be disabled like I was able to install almost everything previously.

Tried also this hack and it doensot work:
Disable Driver Signing in Windows 7

Bump, nobody has an idea?
The particular driver I have the restrictions on is latest Intel HD Graphics driver beta - https://downloadcenter.intel.com/De...&OSVersion=Windows 8.1, 64-bit*&DownloadType=
This was installable on previous OS instance.
The message it gives me is

Error: Installed driver is not verified for this computer. Request appropriate driver from computer manufacturer.
Setup will be terminated.

Click to expand...

Anybody can test the error?

hmm to disable driver sign reinforcement in windows 8 all u have to do is an advanced startup
and just press the corresponding key to select disable signature reinforcement !

This is what I did, F7 on advanced startup. The error is appearing still.
Is the change persistent or one boot only?
OS platform and build is exactly same (Win 8.1 Enterprise), hardware is exactly same.
Does the error mean something else than driver signature problem? I'm 100% sure that present GPU model is listed in supported HW:

This software driver package will install the Beta Intel® Iris™ and HD graphics driver for:

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4th Generation Intel® Core™ Processors with Intel® Iris™ Pro Graphics 5200 4th Generation Intel® Core™ Processors with Intel® Iris™ Graphics 5100 4th Generation Intel® Core™ Processors with Intel® HD Graphics 5000/4600/4400/4200 3rd Generation Intel® Core™ Processors with Intel® HD Graphics 4000/2500
....
..
.

Click to expand...

are u sure it matches ur chipset?

Yes sure. If it didn't match it probably wouldn't install already on previous OS instance.

sri2000 said:

hmm to disable driver sign reinforcement in windows 8 all u have to do is an advanced startup
and just press the corresponding key to select disable signature reinforcement !

Click to expand...

That only works for that one boot up. On the next reboot it goes back to normal and the driver won't load. I've done it in the past and never found a way to make it stick for every boot up. Not in Windows 8 anyway.