The rusted pipe is a press fit into the bottom half of the inlet plenum, so with a bit of difficulty you can crush it inwards and remove it, then if you know a machinist you could get them to make up a new piece with the right tolerances to press in. I have been told you can buy this piece but I couldn't find one, there's no part number for it in FAST so I doubt you would get it from Nissan. So it would probably end up being easier for you to buy a new inlet manifold.