No. Must be new. They are vin locked. Once a vin is programmed it cannot be changed.
There may be after-market add-in modules available for the base radio if you're just after XM, Bluetooth audio or a line-in. The OEM Nav is a long-way around to get that. While it may be the easiest way to get Nav, full functionality may not be a practical (cost effective) goal. Members advising trading for another STS to get desired features are making a valid point.
I'd say the way to start is to be sure what's most important to you and then evaluate the alternatives. Unfortunately, the STS wasn't sold/produced in large enough numbers for a lot of aftermarket solutions but members have found several. If all you want is XM, there are several ways to get there: (it was available on base & nav OEM's and then aftermatket options). If your heart is set on a full-blown system, I remember reading a post from a member who found a module that would let him store the base car settings without keeping the radio. (That may not help owners that want to replace their OEM nav but it solves that concern for you.)
Then it's just a matter of getting plugs wiring it up as having the module added to the can bus system via tech 2.
There is also the matter of the xm aerial which I believe is in the shark fin, which may or may not be there. I'm guessing not. The shark fin also houses the Onstar aerial.
I think all STS came with the rooftop antenna; which style is a different story. This car is the opposite of an easy mod.
I should have made my response clearer. They all have the shark fin, whether or not both aerials are in there, is what I meant.
Agreed. If the XM antenna isn't there, it's no small task.