Basically how christians have always operated since they first emerged and started doing the same throughout the hellenic world. Most (all?) christian traditions are pagan in origin. The main goal was not necessarily replacement but a sort of corporate ownership takeover of the littany of existing traditions, such that these cultures might be ingrained into a unified fold of christian power/influence/customs/laws/expectations and not see themselves as some distinct independent people. And boy that model worked to tame europe and much of the known world under the whip of the pope in a way the roman emperors never could, at least until Martin Luther screwed up a bit of that unity.
Mexico is interesting because it is a certainly a different catholicism than what is practiced elsewhere. Tell a devout old world European catholic about say Day of the Dead traditions and they will probably think its blasphemy. There is a lot of what amounts to local diety worship still as well, although they just label them as some patron saint of somesuch to preserve the veil of monotheism.
Mexico is interesting because it is a certainly a different catholicism than what is practiced elsewhere. Tell a devout old world European catholic about say Day of the Dead traditions and they will probably think its blasphemy. There is a lot of what amounts to local diety worship still as well, although they just label them as some patron saint of somesuch to preserve the veil of monotheism.