Provide a discount for members who are expired

pmpro-discount-pricing-for-previous-members.php

function custom_renewal($level)
{
	global $wpdb, $current_user;

	$levelshistory = $wpdb->get_results("SELECT * FROM $wpdb->pmpro_memberships_users WHERE user_id = '$current_user->ID' ORDER BY id DESC");
	
	if($levelshistory && $levelshistory[0]->status == 'expired' && $levelshistory[0]->membership_id == $level->id)
	{
		$level->initial_payment = ($level->initial_payment/2);
	}
	
	return $level;
}

add_filter("pmpro_checkout_level", "custom_renewal");

This recipe is included in the blog post on "Offer Expired and “Old” Members a Membership Renewal Discount for Coming Back" at Paid Memberships Pro here: https://www.paidmembershipspro.com/offer-expired-old-members-membership-renewal-discount-coming-back/