BuddyPress.org

The tutorial I read about child themes here: https://codex.buddypress.org/theme-development/building-a-buddypress-child-theme/ says you cannot have a functions.php file in the child theme b/c it conflicts with the real functions.php file. So it says to rename it. To your second point, that is exactly what i want to do. I WANT to override the default functions.php file b/c I want to change the default header size. But since the default header size DOES exist in the default functions file you are saying I cannot override it with a child theme?