What an unusual thread. Why would anyone really mod a ///M when it costs so much, is probably still in warranty and likely bought by people who buy it in the knowledge that BMW get it about right with the ///M versions? Touch an ///M and I bet it drops in value like a stone and becomes unsaleable.
I suspect ///M's will largely always be kept 'as-is' (unless taken to the circuit for serious use) enjoyed, driven hard, well maintained and then gracefully age to be collectors cars.
If you want mods I've done a few - not an ///M but a project car (and chucked about 3000 posts in):
A few Modifications from roughly front to rear:
2006 ‘facelift’ front end
Custom clear indicator lenses with CCFL angel eyes
Narrowed number plate and mount to match registration
Clear side repeaters
Carbon fibre badges throughout, bonnet, sides, boot, wheels and steering boss
Alutec triangulated Strut brace
Air horns
Custom ‘smoked chrome’ 108’s
Falken tyres and OEM mobility unit to replace RFT’s
‘Big brake’ conversion to 325mm slotted and vented EBC discs, red calipers and greenstuff pads
Reinhold remote roof/window opening and 1 touch roof modules.
Sound insulation in doors and large panels
MFSW for audio, phone, Sat Nav. Etc.
Paddle shifts to control Steptronic auto box
Cruise control module
Dream red ///M sport seats on electric memory and heated bases
Matching dream red door cards
Aftermarket Door speakers
Illuminated ‘Z’ sills
Second under seat storage box on driver side
Alloy pedal covers
Door LEDS inner and outer handle and LED puddle lights, controlled by auto dimming system
Bluetooth phone retrofit module and column microphone
Hardtop (not really a mod, but not a standard fit)
White spot rear lights
Clear third brake light
And cupholders are on the parts desk at BMW to collect and a ///Msport rear is about to be delivered for a quad conversion