From OEM parts it looks like the license plate lights are one piece (#1) - Plate Illumination. #2 is totally a separate piece. I am guessing (without looking) that #1 fits in from the inside or is attached on the inside with the lens cover removable from the outside to change the bulbs. With the plate that both lamps site on adjacent to the opening the cam would have to sit in the area of the plate or you would have to cut the plate to fit the cam. It almost appears that the cam itself would be the same size as the lens cover therefore a "clip and fit" Historically I looked at the E46 rear view cams and mostly folks had drilled a hole adjacent to the license plate and just fitted the cam in that way (this was years ago though). So a couple of things relating to the camera. 1 - it should be same size as the license plate lamp lens cover. 2 - retrofitting existing license plate illumination "plate" to accomodate cam. The second part would be easiest to do buying a new part and trying to modify it.

I looked a couple of different vehicle OEM cameras (on OEM parts dot com) and it looks like all of the cameras typically mount inside to the outside adjacent but not above the license plate frame (like where drilling would be involved) from the style (not sure if the style in the pics is the actual camera).

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1