Even if you split your script into pieces you can't run a script per level. When you split your script into individual files and add them using #include, the engine merges it into one.

Define your variables like this...

var ammo = 150;
var health = 100;
etc

and then when you load a new level with 'level_load' they will still be the same. If you want to reset them I would write a function to do that and then call that after level_load...

void ResetSettings()
{
ammo = 150;
health = 100;
}