You should not want to (or try to, for that matter) change the
build-files.zip, it was split of from the
html-design.zip for the reason to keep the
html-design.zip, simple, manageble and usable.
fonts folder and its content will not be automatically copied to the
dist folder of the Grunt build. This all depends on the references you make to the fonts in there. Bootstrap references its fonts in its Less files, and those are downloaded via Bower I think. I’m not too much of an expert on Bootstrap, since I’m not a front end developer myself, so I don’t know too much of those details. I would dig through the Less files (certainly those of Bootstrap and Bower) and check if you can find font references there, and see if you can change them to your desired font.
The DXA HTML Design is a bit limited in the sense that we don't allow you to change the
bower.json (these are overwritten by the contents of the
build-files.zip at publish time). If you can't make your desired changes without adjusting the contents of the