BuddyPress.org

Here is a way to kind of do it

in the main plugins folder add this to a custom-code.php file

function custom_group_alpha_first() {

?><option SELECTED value="alphabetical"><?php _e( 'Alphabetical', 'buddypress' ) ?></option><?php

}

It will work, but then you have duplicate Alphabetic selects. You can try to hide the other one with CSS or Javascript using the DOM. good luck.