The changes made to the pwoertrain ot attain ULEV and SULEV are mostly related to cost than specifically engine performance. A manufacturer might use a more expensive O2 sensor or multiple sensors to achieve tighter control o nteh air/fuel ratio. The second change is a more expensive and/or complex catalytic converter. Some Cat's cost more because they contain more of one or another perticular metal catalyst and may have a more restrictive design to achieve more complete conversion of certain emissions.

TO control manufacturing costs, I wouldn't expect there to be any mechanical changes to the VTEC. Only small changes to the fuel mapping or program.