Game mode solved?

Until Game mode is implemented I guess I found a way to get rid of that black screen. Credit is not mine but ace55 on wilders.

All you have to do to prevent this black screen, however, is create a predefined rule allowing an interprocess memory access to c:/windows/system32/csrss.exe and apply that rule to every fullscreen game before you launch it. You have to open the CIS UI, add a new application to Defense+ manually, and then apply this predefined rule to it.
It would be easiest if Comodo simply modified the default configuration to allow all applications to access csrss.exe in memory. In fact, you should probably do this instead of my suggestion above. There is an all applications rule under Computer Security Policy which you can modify. If you add the interprocess memory access to csrss.exe here, it will globally allow it for all applications.
I've tried second method and yesterday Sniper Ghost Warrior Demo launched perfect fine. I don't have other games installed ATM but for first attempt looks fine. Seven x64, FW and D+ in Safe Mode, Sandbox enabled.