Can be done by using Volvos VST (hand held scan tool) to re-program the trip computers values BUT it'll cost you whatever the dealer wants. I can't tell you a cost as I've never been asked to do that to a car out of warranty as most people are then no longer that concerned (not enough to pay).
One thing's certain about trip computers as I've heard more complaints about them with S80s than older cars like yours, be sure to read what's mentioned about it in your owners manual because they're not 100% accurate at best, they average you mileage and with S80s, the average is based on the last few miles of sampling, not the last time you filled the gas tank so it won't be an exact same amount no matter what.
If you've ever changed tire size from what was originally on that car (for example), that would change the trip computers accuracy and cause it require re-programming.