They're already an invasion force, and they haven't needed formal troops. If the Mexicans are that numerous in the area and unassimilated, the answer is yes. Besides which, it's not the same. The Mexicans have a better life as part of the US, and they're not living under a government installed by coup.
The answer before these hypotheticals happen is like I said to put our troops on our southern border and send home the invaders before they cause our downfall. Look at history....bringing in cheap labor didn't work out real well for ancient Rome.
I was responding to your earlier assertion, please don’t move the goalposts.