Vehicle License Tax Act Article 14

When changes such as replacing parts or altering seat frames occur in the transportation equipment already licensed for use, the owner or user of the transportation equipment shall proceed with the necessary changes through the traffic management authority. If the tax amount remains the same before and after the change, no additional tax shall be levied. If the transportation equipment, originally exempt from tax or subject to a lower tax rate, is changed to a taxable status or a higher tax rate, the additional tax amount for the difference shall be calculated on a daily basis. Conversely, if the transportation equipment, originally taxable or subject to a higher tax rate, is changed to an exempt status or a lower tax rate, the tax amount for the difference shall be refunded on a daily basis.Failure of the owner or user of the transportation equipment mentioned in the preceding paragraph to proceed with the necessary changes through the traffic management authority, and failure to pay the required taxes as stipulated, shall be considered as a transfer of the license for another use.
中文原文 使用牌照稅法第14條
已領使用牌照之交通工具發生改換機件或改設座架等,應由交通工具所有人或使用人向交通管理機關辦理變更手續。
變更前後應納稅額相同者,免再納稅;原屬免稅或原納較低稅額之交通工具,變更為應稅或應納較高稅額者,應按日計算徵收差額部分之稅額;原屬應稅或原納較高稅額變更為免稅或應納較低稅額者,應按日計算退還差額部分之稅額。
前項交通工具之所有人或使用人,不向交通管理機關辦理變更手續,且未依規定補繳稅款者,視為移用使用牌照。

English translation for reference only; the Chinese text prevails. Not legal advice.