You can change all those parts without really effecting the tune much. The BOV is not really something he could tune out so really, it's tuned for a recirc one already most likely (as he started from cobb maps). The intercooler can be changed without effecting anything but your not going to see GAINS unless you push the tuning a little bit.
As for the stock STi intercooler being bigger than the XS-power one, I have no idea. Never heard of the XS-power brand but I can tell you that the STi intercooler ain't that big to begin with. I'd forget this suggestion as the new purchase, labor on swapping, and dyno time to re-tune would be $$$ for at most very small gains.
I'd just stick with what you got until your stock turbo starts to bother you. Then, go in with something a lot larger like a Perrin TMIC or a FMIC if you prefer.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD