make a backup first so you can put it back to its original format.
After replacing the .exe file of the game by the .exe file coming with the trainer, the game starts to load but freezes before the main screen
Not sure how to help you more than we are..
replaced that file here:
C:\Steam\steamapps\common\Sniper Ghost Warrior Contracts
Run game from steam
Activate at main menu
Nothing more to explain