Effects of the POD
Well firstly, Scott didn't land in Veracruz until March 1847, a few months after the fall of Monterey. So in my opinion, if Monterey had repulsed its attackers or held out longer at least some, if not most, of Scott's forces might have been diverted there. This would most likely postpone the amphibous assault on Veracruz and give Mexico the opportunity to draw the Americans into a slugfest through nothern mexico, which might be enough to result in either a negotiated piece in which they hold on to significant parts of new mexico or exaust the Americans enough that they are ripe for a counterstrike- in montainous terrain where the U.S advantage in artillery is partially neutralized.
But I'm interested in everybody's opinion, so please feel free to disagree with me as long as you have ideas as to what would happen following the initial POD.
Kingp