[Correlli]

You don't need to change the core files.

Example:

pawn Code:

stock AddVehicle(modelid, Float:spawn_x, Float:spawn_y, Float:spawn_z, Float:angle, color1, color2, my_param)
{
  new
      vehicleID = AddStaticVehicle(modelid, spawn_x, spawn_y, spawn_z, angle, color1, color2);
  myVariable[vehicleID] = my_param;
  return vehicleID;
}

I haven't tested this, i guess you'll need to that.

If this is what you want?