Assigning another membership based on first registered membership

code.php

<?php

add_action( 'ms_model_relationship_create_ms_relationship_before', 'ms_controller_member_assign_memberships_done_cb', 99, 4 );
function ms_controller_member_assign_memberships_done_cb( $membership_id, $user_id, $gateway_id, $move_from_id ) {
	$target_membership = '';
	switch( $membership_id ){
		// if first membership 123
		// then assign to 456
		case 123:
			$target_membership = 456;
			break;
		
		// if first membership 321
		// then assign to 654
		case 321:
			$target_membership = 654;
			break;
		
		//and so on...
	}
	
	$member = MS_Factory::load( 'MS_Model_Member', $user_id );
	$subscription = $member->add_membership( $target_membership );
	
	if ( $member->has_membership() ) {
		$member->is_member = true;
	} else {
		$member->is_member = false;
	}
	$member->save();
}