Well I just got a large cam, milled heads, a valve job, and headers in my Z got the cats with the headers so the car was tuned that way. As soon as i get the car I am umm having a magician play with my car and i believe the cats will wind up empty haha. but I wanted the canisters there for umm sound you know
Anyways my tuner says that I do not have to worry about a retune when that happens.
I believe that because before I had an 06 gto that i did the same thing too with the same tuner then drove 3.5 hours to have the tune checked since i went from cats to no cats. I picked up like 6-8hp and he didnt have to touch the tune so in that respect I say you are fine however i dont know if FI changes the equation.