When you load a world you can choose the Textures/Sounds/"Language" you want to use. So if someone plays your map he will be asked if he wants to download the stuff. You can also add your own Textures/Sounds/"Language" to the world, they will be saved in the world folder, so you can:
- redesingn blocks and items
- change sounds
- change names("lever" is called "key")
Of course the packs would be checked whether they are only media or if any virus activity is there. So no code has to be checked, only whether there is any strange code.