HL1 - Gamma and Brightness cvars do not work! :( Thread

I see many players playing with well stylized CFGs, with illuminated maps, no shadow, etc. I noticed that most use "gamma 10" and "brightness 10", but when I try to use these values, the game doesn't let them go outside the default (3 and 2, respectively). I can't find solution to solve this obstacle. I tried everything: using autoexec.cfg, using userconfig.cfg, I installed the game on drive "D", etc. Nothing works. Can someone help me?

p.s.: My hl is original from Steam.