The requirements of section
7586 of this title may be met through the conversion of existing or new gasoline or diesel-powered vehicles to clean-fuel vehicles which comply with the applicable requirements of that section. For purposes of such provisions the conversion of a vehicle to clean fuel vehicle shall be treated as the purchase of a clean fuel vehicle. Nothing in this part shall be construed to provide that any covered fleet operator subject to fleet vehicle purchase requirements under section
7586 of this title shall be required to convert existing or new gasoline or diesel-powered vehicles to clean-fuel vehicles or to purchase converted vehicles.