This is helpful. I think my plan here is ultimately to do a sports cat (not a full decat) and a Borla axle-back exhaust.
Specifically, looking at: https://www.ecstuning.com/b-milltek-sport-parts/downpipe-with-high-flow-catalytic-converter-oem-exhaust-fitment/ssxm429~mll/
I would do a Stage 2 tune through Dinan at the same time, so the coding shouldn't be a problem. Would that pass, do you think?