Change user's membership level only when a user expires from a specific level.

change-level-only-when-user-expires.php

<?php
/**
 * Change membership level within the Paid Memberships Pro expiration code (this does not affect manual cancellations at all).
 * User's will still be able to cancel their membership level after their expiration level change or before.
 * Please read through each line of code and adjust the level ID's found inside pmpro_changeMembershipLevel() function accordingly.
 * Add this code to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 * 
 * www.paidmembershipspro.com
 */

function pmpro_set_default_level_only_when_expiring( $user_id, $level_id ) {

	global $wpdb;

	$SQL = "SELECT membership_id FROM $wpdb->pmpro_memberships_users WHERE user_id = $user_id AND status='expired' ORDER BY id DESC LIMIT 1";

	$results = $wpdb->get_results( $SQL, OBJECT );

	$expired_level = $results[0];

	$old_level_id = (int) $expired_level->membership_id;

	// If there is no previous level they are expiring from, let's just default to level 1.
	if ( ! empty( $old_level_id ) ) {
		// check what level they just expired from.
		if ( 3 == $old_level_id ) {
			pmpro_changeMembershipLevel( 2, $user_id );
		}

		if ( 5 == $old_level_id ) {
			pmpro_changeMembershipLevel( 3, $user_id );
		}

	} else {
		pmpro_changeMembershipLevel( 1, $user_id ); // If no previous level is found, default to level 1.
	}
	
	return $user_id;
}
add_filter( 'pmpro_membership_post_membership_expiry', 'pmpro_set_default_level_only_when_expiring', 10, 2 );

For assistance, please open a support ticket on www.paidmembershipspro.com/support