Is the 02 sensor different? -- This is the only way a computer would know you have a new cat.

I would see if an exhaust shop can modify the regular cat to fit.

The ludicris price for the ULEV cat is insane, You may be cheaper just convering you entire exhaust to the standard Accord.

You only need the B-pipe manifold and CAT. Maybe you could also convert to a header and aftermarket cat for cheaper as well. Or get the other parts from someone that has already got a header on this board. I see about gettting a used exhaust system from a junkyard as well.

I'd also call Honda of America, the CAT may be covered under 80,000mi or 8yr emmission equipment standard as well.