Just to go out on a limb here but I don't think a tune would fail emission even for here in CA unless cats have been deleted and you upgrades that make you fail visual inspection then the actual test itself. Since emission testing is done in the range of 2250-2700 rpm, I don't think any tunes affect standard emission in that range especially since there are no loads during the test.
Was it an actual ECU swap out or was it an ECU port flash ?

 

Can you pm me the vin # of the car? I can check what program you have. Typically we would have sold a durametric cable to the original owner or the car would have been flashed by one of our dealers with the same cable. Ask the owner if the FVD flash cable comes with the car. Then you can simply flash the car back to stock and pass the emissions.

However it depends on how long ago the software was written so the Vin # can help me determine exactly what you have. By the way you don't need to purchase an ECU at all. All of our flashes can be overwritten by the dealer with the PIWIS if you needed to.

 

Aha! I think I get it. The listing states "FVD Brombacher ECU upgrade w/ programmer". So I guess that would allow me to put the stock tune back on if I need to.
AFIK, there are no physical changes, just the ECU programming.
Things are looking promising...

 

Yes. If the owner gives you our My Genius programmer you can flash back to stock as the stock file resides on the programmer. But if they used the Flash Client (durametric) cable make sure that the owner emails you the original and tuned file or has it on a flash drive or disc with the car.