If a bunch of liberal white Catholics move to a conservative white Catholic area and cause the area to go rat, that's certainly a demographic change IMO.
The demographic shifts we see now are the former hispanic types --- those SW USA hispanic types, added to later by those fleeing the Mexican Revolution --- the old Conservatives of Mexico with the type from the southern states of Mexico or from the slums of Mexico City --- not rancheros, not hard workers. Ciudad Juarez itself complains of this type of demographic shift going on there --- not long ago it was a quiet desert town --- but in a couple decades all sorts of people moved in with no roots in the north. People cut off from their southern villages and families, extremely poor people unaccustomed to northern desert life -- the extreme heat and cold. That is also a demographic change --- not a healthy one.