Re: change root directory
Actully, I didn’t pay attention on the fact that you are on WPMU, for which I got no experience so far.
Anyway, if I am not wrong, you can put the code in “functions.php” in your theme or child theme, or have a file (create one) called “bp-custom.php” and put that in the plugins directory, not “buddypress” directory, just in the “plugins” directory.
That will act like a plugin.
Try and let me know.