Once someone asked in this forum with no answer. After days of trying, I figure it out now, although not quite perfect. (Hope there's still someone interested...)
1 Build the NTe run-time image, but don't boot from it.
2 Use regedit.exe to load winn\system32\config\system and syste.alt, change these keys:
In [SYSTEM\ControlSet001\Control\ProductOptions]
Delete "ProductEvalInstallTime" an 'ProductSuite';
Remain "ProductType" as WinNT
In [SYSTEM\Setup]
change "SystemPrefix" to hex:d9,13,00,00,00,20,50,58
This will hoax the sytem to believing that it's full version of Windows NT 4.0 Workstation. Of course I get this combination from NT4 workstation installation.
3 Boot from your run-time image, try to set the date several years later, reboot. See, desktop is still there!

Replacing it with the combination from NT4 Server is also feasible, and other version should work, too.

If anyone has a full version of NT4 embedded image, Please share the combination (together wih [SYSTEM\ControlSet001\Session Manager\Executive]\PriorityQuantumMatrix, which is not necessary but may be specific for each edition) and so we all can build real full version of NTe by this kind of registry tweak!

I don't think this is the right place to make such posts... Is it?

Should probably be moved to the "Tutorials and Guides" section under General Discussion. JiaShang, you can ask a moderator to move it for you.

What is a Timebomb in Windows NT? Sorry for the Question but i dont test it

Marvin344, are you seriously telling me that you can't find out for yourself?

BetaArchive is not the place for asking such basic questions.