Code-Snippets-Functions/Execute a function on a child site/BuddyPress/disable-buddypress-registration.txt

function bp_disable_bp_registration() {

    if ( is_user_logged_in() ) {
        return false;
    }
	remove_action( 'bp_init',    'bp_core_wpsignup_redirect' );
	remove_action( 'bp_screens', 'bp_core_screen_signup' );
}

add_action( 'bp_loaded', 'bp_disable_bp_registration' );