BuddyPress.org

It is bad practice to edit the Buddypress Default theme that ships with the plugin itself, because the next time you update, all of your customizations will be lost. That is, obviously, a bad thing.

To make a child theme, just create a new folder with your FTP client at the same level as your bp-default and bp-sn-parent. Call it bp-whateveryoursiteiscalled. Copy the contents of bp-default to it. PRESTO, you have a child theme! Select that theme in your dashboard, and any changes you make will be live right away.

Now you can copy whatever files you want from bp-sn-parent to your new child theme (preserving directory structure, if I’m not wrong) and edit them (ie, in this case, header.php). Any files you do not copy and change will stay ‘stock’. And next time a new version is released, you can upgrade with confidence and any changes you make will persist.

Child themes are a godsend.