They sell you a bumper M kit for 14K and you think oh cool, not too bad.
I fell into this trap with my previous E39
This conveniently misses the other 14K parts - Paint, fogs, lower grill, under tray, front radiator lower shroud, brake ducting, fender liners, Lower triangle plastic covers, bumper brackets, bumper rubbers, matching side rubbers, fog light connectors, alternator vent ducting and the list goes on.
It is possible to cut what is already there but this makes for a really K@K upgrade as you basically have to butcher the Hell out of the car, you may as well fit a Honda bumper easier.
Do what I did to mine - ask for the BMW E39 "Aerodynamic package", made by Zender and it clips on to the existing bumpers, looks awesome and not too pricey