What is the effect of lard in tortilla dough? Can a vegetable oil of preference be substituted for it?
Rendered pork fat—manteca de cerdo—is our preferred cooking fat throughout this book. Lard has a relatively high smoke point so it is ideal for frying, and it provides a richness, dimension, and distinctly Mexican flavor that you just can't replicate with using other fats...Vegetable oil is a fine substitute
However specific recipes may really need lard:
Note that the flaky texture and slight richness that make flour tortillas so compelling are derived from lard. I've found that vegetable shortening is a poor substitute here...
Source: Alex Stupak and Jordana Rothman. "Tacos: Recipes and Provocations".
I have found that using lard to make tortillas allows me to shape them more easily with a rolling pin, because it becomes a very workable dough just with handling at body temperature.
I would not use vegetable oil as a substitute, Crisco or another vegetable shortening would make more sense. Definitely don't use butter.