I think it might be part of one of the sport aero packages perhaps.
On non-M cars, this always looks to me like someone stole the BMW's
grill during the night, but then tastes do differ.
Still, it's easy enough to replace the grilles as they are literally
just snap in place and cost peanuts to replace ('peanuts' being $12 for
an 'official' replacement chrome insert on an E46 coupe).