Any chance you can say where to change it in a Less variable?
Using the mixin method of building the bootstrap grids makes Bootstrap as semantic as you want, even moreso than semantic-ui. Not saying it's bad, but people run to bootstrap and say "look, you have to set it up like 'div class="col-xs-5 col-sm-6 col-md-7 col-lg-8"!!' When in fact, you could just go 'div class="top-stories"' and then all the grid sizing is handled in the Less mixins.
So in a way, Bootstrap can be more semantic since there are no limits to how you want to name things and how much you want to throw into the Less mixins.