Notwithstanding the provisions of subdivisions 1, 2, and 3 of § 58.1-3506.2, the governing body of a county, city or town may by ordinance specify lower income and financial worth figures. The governing body also may prescribe by ordinance for a maximum amount of tax relief hereunder based on the assessed value of the motor vehicle or a formula which takes into account the income and financial worth levels of the individual seeking the benefit of the preferential tax rate. The Department of Taxation shall develop a model ordinance to assist local governments with the implementation and enforcement of this article.