16 Pa. Stat. § 4902-A
A county of the second class or a political subdivision located within a county of the second class may, by adopting an ordinance or resolution, utilize the tax-neutral assessed value when levying the real property tax on the homestead of a qualified owner-occupant after a mandated county-wide reassessment. For a county-wide reassessment that becomes effective in 2000, such ordinance or resolution by a political subdivision located within a county of the second class may be adopted at any time prior to June 30, 2002, and may be retroactive to no earlier than January 1, 2001. In the event that such resolution or ordinance is adopted retroactively after real property taxes are levied during 2001, the levy shall be adjusted for qualifying homesteads as if the resolution or ordinance had been adopted before real property taxes had been levied in 2001. Any overpayments of real estate taxes which arise from this adjustment shall be refunded by the political subdivision.
16 P.S. § 4902-A