It's possible yes, but not at all 'easy'. First you would have to get the new northbridge and remove the old one without killing your motherboard. Then you would have to solder in the new northbridge and reconnect all of the traces on all of the PCB layers.
And I'm almost certain there are probably other difficulties that I'm not aware of, not to mention the BIOS would have to also be specifically updated to handle this "conversion".
So I'd have to say yes is IS that technically difficult, and not at all something likely to happen.