I would change the front and side indicators to clear, and the bulbs to silvatech so there's no orange. I would change the rear clusters to a smoked set. I would have traction control, and a switch for the suspension, just to change it from comfort, to road holding. I would love those wheels Ruud sugested, but polish the rim, and paint the centres to match the car (Gunmetal Grey)and some bigger brakes all round. De badge just the LS400 and leave the Lexus 'L' in place front and rear. Have a light tint on the rear windows, and change the stereo for a car pc with a 10" multitouch screen in the front, and screens in the headrests, Sat-Nav etc... Change the electric ariel for a small understated sharkfin antenna for satnav/radio/phone.
Oh, and put it into a garage, and get EVERYTHING checked over, and replaced if worn, and the entire bodywork given a good going over, and respraying in the same colour. And the same for the interior!
Maybe a BMW V8 stuck in the front?
And a full valet, and change the carpets, and upholstry...
Just a bit of TLC really... lol
Brian :)