I'm still struggling...

A "power tune" shouldn't affect your emissions testing result as the driver is never really 100% throttle and high enough RPMs (for us to even get into vtec too), even if the tuner has opted for max power at cruising conditions, the fuelling won't be anywhere near ~12.8:1. (assuming peak energy mixture for gasoline)

What were the reasons for being knocked back with cat/exhaust, etc etc?