Adding fog lights to the 453 is a 3 part situation. You have to:

1 - Fit the fog lights and the wiring loom.
2 - Code the fog light ability.
3 - Fit the replacement stalk.

Step 1 - Fit The Fog Lights And Wiring Loom

Remove the front bumper.



Use a Torx25 bit to remove the screw holding in the fog light blanking plate.



You'll need replacement panels from a smart dealer. On the fortwo, the smart part number is:
A453 826 06 00 - This will get you a pair. 1x left, 1x right. These were only £13 for the pair when I bought them.



On the forfour 453, the parts are different so the part numbers are different. If you want the numbers, ask me. 



You have an option. Standard halogen fog light units or LED fog light units. More on these later.