No, they can come activated.
Here is the deal:
You order rear airbags (~$400 option). You now have the choice of whether or not to have the rear airbags turned on or kept off. That is part of ordering them on the car in the first place. When I ordered my car, I had them turned off. (In hindsight, I probably should have skipped the option althogether....). As of today, they are still off.
If you have small children who are a certain age or a certain size (height/weight), you may wish to have them off and then activate them later on when they are older/bigger.
If you want them turned on, the door panels must be removed and the airbags physically plugged in. Then it must be coded via the computer. This no big deal if done when you order the car but there is some labor involved if you do it post-production.
Also, you can probably get it done for free if you are buying a CPO'ed car with the rear airbag option.