convert_to_lifetime.php

<?php
require './wp-load.php'; // only necessary if you run this script on the command line

$membership_id = 8888; // Change this to whatever your membership_id is
$m = new MeprProduct($membership_id);

$subscription_table = 'wp_mepr_subscriptions'; // change this to whatever your subscriptions table is named

$q = $wpdb->prepare("
    SELECT s.id
      FROM {$subscription_table} AS s
     WHERE s.product_id = %d
       AND s.status NOT IN ('pending','cancelled')
  ",
  $membership_id
);

$sub_ids = $wpdb->get_col($q);

foreach($sub_ids as $sid) {
  $s = new MeprSubscription($sid);
  if(!$s->is_lifetime() && !$s->is_expired()) {
    $txn = $s->latest_txn();
    if(!empty($txn) && $txn instanceof MeprTransaction) {
      $txn->expires_at = MeprUtils::db_lifetime();
      $txn->store();
      error_log("Changed Subscription {$sid} to lifetime by setting Transaction {$txn->id} Expires At to {$txn->expires_at}");
    }
  }
}