i think one of the few like. deliberate genetic modifications humans in my setting have done to themselves thats actually made its way completely into the gene pool (to the point that most are born with it) is a change to tooth growth:
specifically, rather than growing only two pairs of teeth and being stuck to deal with the last set for the rest of one's life, teeth fall out every 5-7 years as their replacements grow in.
it's generally considered important to eat plenty of tougher foods as the new teeth come in and the previous set come out, in order to ensure they don't grow in crooked
also the diets of these humans are generally slightly higher in calcium-rich foods to make up for the fact that new teeth are constantly, if slowly, being grown