Well, cracked open the hptuners today for the first time in 3yrs since the car set off the p0420 code after about a week with the new cat. Solo sent the extension piece but the o2 would hit off the frame if i used it with the new cat-back since the bung is slightly angled. The mid-pipe must have been an off day for the welder. 
Anyway, on my last car, I just had to go into the dtc section and set it to not report and that was it. When I pulled the file from the saturn, there is also a post cat disable in the regular engine section. Would just disabling the post 02 check take care of it or do I need to change some other stuff?
Also looking through the rest of it, I have alot of learning to do. I think my brain melted a bit. This is like a supercomputer to the abacus that was the regals pcm. 
All you need to do is disable DTC 0420. Since you are still running a cat (even a high flow) you'll still want all the COT protection on. So don't disable those.
As for whether emissions will notice. Depends. Some areas don't do a readiness check, but only a sniffer, and a lack of DTC codes logged. So as long as you reset the 0420 DTC, and then set it for say 5 occurrences before it logs a code, it would pass.
These days, I'm running a punched out stock cat, which I'm considering putting a second wideband A/F onto, and a gauge. And in about 4 years when I have to pass a sniffer test, I'll simply put my original stock cat back on for the test. And then put the punched out one back on, with some new turbo studs and high-temp anti-seize. I've already removed and put back on the downpipe/cat many times. I could probably use new studs by then.
I put in a new tune this last weekend, and my fuel trims are WAY off. I've basically disabled my long term fuel trims. I should start data logging my daily commute again to get the fuel trims closer again.
