yes you can. (for the trim) i dunno about the BMW assist.
If the dealer wont let you, you can order the trim separetly at your own time. check www.circlebmw.com
My car came with the premium package 'wood' and soon ordered the matteChrome trim from circle bmw for $405 (coupe) and installed it myself.
if you have a sedan, "Brushed Aluminum" is not offered from BMW...from my sources. But if you have a coupe, you can get the brushed aluminum. Let me know what you like and ill get you part numbers.
popular ones for coupes::
MatteChrome: pretty much aluminum
Titan Shadow: darker style of MatteChrome
Brushed Aluminum: Real aluminum with brushed grains
silver cube: silver carbon fiber looking
black cube: black carbon fiber looking
EDIT: forgot to mention, if you have a couple, i need to know what color interior you got cuz the trim come in whole units, meaning the underside of the trim pieces are matched to the interior of the car.