No, you can't turn a Pontiac Fiero into a hardtop convertible in the way that term is usually understood. A hardtop convertible implies a retractable hardtop roof, like those found on some luxury cars. The Fiero's body structure isn't designed to accommodate that kind of mechanism. The roof is an integral part of the car's strength and rigidity.
You could, however, *remove* the Fiero's targa top (if it has one) and create a more open-air experience. But that would leave the car as a targa or roadster, not a hardtop convertible. There's no feasible way to add a sophisticated, power-operated retractable hardtop to a Fiero without a complete and incredibly complex chassis redesign.
