Ignore Damage (Perfect God Mode)
This acts <like> the cht_bGod=1 + cht_bIgnoreDamageInGodMode=1 combined. At least that's the effect. Note the "like" - it doesn't turn cheating on, so you're safe from not getting achievements. In terms of how it's done, I simply flip a bool flag in the CPlayerEntity structure so the Entity becomes non-damageable (similar to Unreal Engine 4's bCanBeDamaged BoolProperty in Character UObject).
Infinite Clip + Fast Fire
The script hooks a spot where the CFireableWeaponMode is read from the current CWeaponEntity. The script checks if the obtained pointer is valid, then if [CFireableWeaponMode+8] == CWeaponEntity (just in case AI would execute this, so they don't benefit from it). Lastly, I get the CFireableWeaponModeParams and adjust various values to meet my goal