A wallhack typically modifies the rendering pipeline by:

injection) are programmed to "hook" into the game’s graphics engine—specifically —and map the "on/off" switch to the Visual Effect

The "F1" cheat typically operates by replacing the game's original opengl32.dll file in the installation directory

Download or compile wallhack.dll. Download or compile dllInjector, which I've forked to https://github.com/zhutoulala/dllinjector,

Critically, Valve’s official Counter-Strike 1.6 already assigned a legitimate function to F1: (buying a pre-configured loadout of weapons). Many false accusations arose because a player’s hand might accidentally brush F1 during a tense moment, opening the buy menu. An inexperienced observer might see the menu flash and assume it was a cheat menu.