@alanchrishughes; It’s not difficult to create a child theme. I’ll try to put it in newbie terms as I’ve become increasingly aware that a) lots of WP and BP newbies seek help here, and b) we’re all newbies until we know something, at which point it becomes “easy and why didn’t I think of that before”..!
As @hnla says, a child theme overrides the core default theme. All this means it that if you create a clone copy of the default theme into your /content/themes/ folder, then make some minor changes so that BP knows it’s a different theme and will let you install it. Once done, all files and functions in it are used rather than the default theme’s, and these are what you edit.
Clone the entire default theme folder from /buddypress/bp-themes/bp-default/ into /content/themes/my-theme (or whatever name). Ie., copy and rename the bp-default folder. Then edit its style.css file and change the settings in the head to something different. Our new theme’s style.css looks like this;
Theme Name: Facelook
Theme URI: http://lincme.co.uk
Description: A modified version of Avenue B2’s Fishbook.
Author: Avenue B2 & LincMe Admin Team
Tags: buddypress, blue, white, fixed-width, two-columns
As you can see, it still uses bp-default as its template, but everything else is different, so BP will allow it to be installed as a new theme. (There’s no default CSS or admin-bar CSS import because I dumped the bar, and just put all of the CSS in the one file). Note: It’s important to keep the ‘buddypress’ tag in there, or BP throws the teddy.
Any files you change in the new my-theme folder and sub-folders will cause changes, and anything you remove will fall back to the bp-default theme’s style and methods as @hnla said. Obviously, if you only need to change a couple of files then you can remove the rest, and the default theme will take care of those parts for you.
Some of us, me included, have variously whined or shouted about the way BP themes work, and yes, finding stuff in files can be difficult to begin with. Once you find the bits you want it’s easy though, and if you make a pig’s ear of something you can always copy the default file back over your cloned one and start afresh.
You may know most or all of this, but it’s for newbies who may shake their heads at the thought of creating a new child theme. Some folks have done gorgeous new BP themes, and added fancy extras in there too. We’ve gone for plain and Facebook-ish for various reasons, and if it’s of any help to you, you’re welcome to a copy. Just email me at any name at our domain. And stick at it – it gets better as you go along!