New exhaust questions

#1
Hi there, I reside in Australia,and ask that you don't hold that against me ..........................

I am contemplating replacing the zorst system on my 2002 G convertible complete with headers and 2.25" ( resonated )
Now, I notice that there are two O2 sensors, one before the cat converter, and one after. Having previously replaced a similar set-up in another car and getting the EMI light, I had to have the ECU reprogrammed to ignore the message to the EMI from the second sensor

Question: when I replace the system on the Astra, can I expect the same ? And, can I extinguish the EMI via the ECU ?

Cheers :)
 
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