Specifically, it patches the Glacier2.exe or Hitman3.exe binary in your system memory (or on disk, depending on the version) to allow the engine to load modified or loose definition files. It tells the game engine: "Do not verify the hash of the package definitions. Trust the user."
The Simple Mod Framework has largely replaced the standalone patcher, integrating the definition bypass into its deployment pipeline. However, the legacy Hitman 3 Package Definition Patcher remains a brilliant piece of reverse engineering—a single executable that opened the Glacier 2 engine to the world. hitman 3 package definition patcher
Sources: Glacier 2 Modding Discord, IOI Forums (Archived), Simple Mod Framework Documentation. Disclaimer: Modifying your executable violates the EULA of Hitman 3. Do this at your own risk on a single-player, offline profile. Specifically, it patches the Glacier2
For the average player who just wants to shoot targets with a default pistol, this article is irrelevant. But for the experimenter—the person who wonders, "What if the ICA Facility had 100 guards carrying flaming swords?" —this patcher is the only way in. However, the legacy Hitman 3 Package Definition Patcher
The Glacier 2 engine calls a function during the LoadPackageDefinition routine, usually named something akin to ValidateDefinitionChecksum . This function compares the computed CRC64 of the current definition against a stored hash in the package header.