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To help cool the blocked radiator you could make a flap to deflect the air from the top of the inter cooler up to the front of the rad. It may be a easy modification. Someone recently was wanting to put clear plastic covers over their fog lights. Someone pointed out that they would become fogged by moisture. Maybe the fog light would shine thru the fogged lens fine ? I think if you are fairly happy with the aerodynamics of the fog lights, i would leave them as is. It's a very nice car, it would not be nice not to damage it with too much stuff stuck on it..
Just use zip ties or tape to adhere your grill block on, if you find the car gets to hot, cut it smaller or remove it, my advice, but hey, you may enjoy making a remote grill cover.