Possible to run game-altering scripts in map?

The question is worded really weirdly, I know.
Is it possible to change certain aspects of the game with codes all centralized in the .bsp of your map? I mean simple things like disabling fall damage or increasing the damage an npc takes from a specified weapon, or making the player regenerate ammo (and not in a stupid way like spawning an ammo pack on the player every five seconds) or something of that nature. It’s been a long time since I figured out how, but I know you can add some entity and give it some keys/values and make it so metro police aren’t immediately hostile, but the difference is that code is in HL2 by default, I want to be able to add custom scripts to the map.

There’s point_clientcommand or point_servercommand. Might work.

Depends on the game. L4D2 features a full scripting system for maps(?) called VScript.

these are simple enough to do without any use of scripts. still, would be helpful to know what game/mode you’re mapping for.

Vscript is implemented for a number of games.

If you’re mapping for GMod, you can use the Lua entity to add fancy stuff.