I suppose in theory it's possible that works. The most likely issue is that the ECU (or one of the several other mini-ECUs spread around the car aside from the BCM, there's a lot of them) only wants to talk to certainly models/revs of BCM, in which case you get some nasty DTC and half the stuff on the car doesn't function, if all of the various bits don't match model/version numbers expected. Could be the reverse too: the new BCM refuses to talk to e.g. your old Airbag controller, or your older IPDM, older ECU, etc...
Assuming everything is protocol-compatible and generally works even with "mismatched" revs, you'd still need a cooperating dealership to do the BCM install, because they have to go in via Consult-III and set a bunch of base parameters in the BCM to match the options on your car when they install it.
All in all, I suspect this just isn't something Nissan cares to support, so it's a crapshoot whether it works out or the car goes nuts and wants its old BCM back. Especially with a big jump like a 2012 BCM in a 2009 car. If someone wants to blow the money and dealership install labor to try it out though, it might be interesting
