The button pieces pop out and are swappable.
If you want the additional controls from the newer wheel, you have to have Ford reprogram your ACM with their IDS system. The sounds & cruise controls will work if your headunit (ACM) is reprogrammed. The SYNC functions obviously won't, since you don't have SYNC.
There's a whole thread about it here:
Base Mustang owners: do you want working steering wheel stereo controls? - Page 13 - Ford Mustang Forums
Basically, you need to change the middle 4 digits to 908B for the Premium wheel, I put xxxx's where the other hexcode would stay the same. It varies from car to car.
727-01-01 xxxx 908B
P.S. I have my Premium steering wheel for sale in case anyone wants its. $50 + shipping.