Supplemental Impact Aid Flexibility Act This bill revises the Impact Aid Program application process for FY2023. Specifically, the bill requires local educational agencies (LEAs) participating in the Impact Aid Program to use the student count or federal property valuation data from their FY2022 program applications, as applicable, for their FY2023 program applications. The program provides funding to LEAs that have lost property tax revenue due to the presence of tax-exempt federal property or to those that have experienced increased expenditures due to enrollment of federally connected children (e.g., children living on Indian lands or military bases).