The last solution is aimed to append new buttons without affecting backend editing panel (customizer). You should manually define the button URL and text manually in the code. It produces the same result compared to backend fields. Code solution is safer as it doesn’t touch any single of file of the theme. Just for your information, editing core theme’s files is prohibited and it’s considered as not a good practice to do. If you wish to do some file changes, you should use a child theme. Unfortunately, adding slide button fields via child theme is a complex task to do, that really difficult to explain in the forum.