2000transamguy

Hows it going, I'm new here to ls1tech...I live in Oceanside, CA. Now to the question. If i get some LT's, catted Y with all the required Air and EGR hook ups my cars PCM will more than likely throw a O2 code.(Correct me if I'm wrong). So i got my LTs on and get it tuned up and everything...2 years later I have to do the whole emission inspection process..I put the stock exhaust manifold, Cats, and Y back on...will this alter the tuning of the car when it had headers...will i have to re-tune it every time i put the LTs back on? Will the car run rich because it was tuned for LTs/Catted Y and now has the stock manifold and cats. If this is the Case I'm better off with C.A.R.B AFR heads and a mild cam, throw some Shorties on there and just tune her once right? I of course will do other mods...but i just want to focus on the SUCK/BANG/BOOM if you know what i mean.(There might be a BLOW in there...i just don't know where) Currently i have SLP Flowpac and LM1 btw thank you SLP for those 2 products. Any input and answers will be greatly appreciated.