Lx to ex manifold and down pipe question

hey all,

the last piece I need to finish the mini me swap is switching the exhaust set up from the lx to ex. I’m under the impression the ex manifold and down pipe flow slightly more for the vtec and also help reduce heat in the engine bay and the cylinder head itself.
i have a stock ex exhaust manifold and will be purchasing the magnaflow down pipe with cat. also going to get the extension wires for the o2 sensors.

I plan to stick with the stock header instead of a stainless one for better heat management (tell me if this is wrong)

finally, my question is for anyone who has done this, will I get a cat efficiency code by doing this? I assume that the lx ecu is going to flip out. if so what did you do to fix this?