Va. Code § 15.2-3817
If a town becomes a city under this chapter, the commissioner of revenue or assessor of the town, if there is one, shall be the commissioner of revenue of the city and discharge the duties imposed on him by the charter or by general law. If there is no commissioner of revenue or assessor of the town, then the circuit court having jurisdiction over such city or town shall, within thirty days after the town is declared to be a city, fill the vacancy by appointment, pending the next ensuing general election or, if the vacancy occurs within 120 days prior to such election, pending the second ensuing general election. The commissioner of revenue so appointed shall forthwith qualify before the court or judge appointing him or before the clerk of the circuit court in the clerk's office. He shall serve until his successor is elected and qualified.
Va. Code § 15.2-3817