Edit the contents of the admin expired email notice.

rcp-edit-admin-email-message.php

<?php

/**
 * Append text to admin expired email.
 * Also convert template tags.
 * 
 * @param string $admin_message Default admin message contents.
 * @param int    $user_id ID number of the expired user.
 * 
 * @return string New admin message contents.
 */
function ag_rcp_before_admin_email_expired_thanks( $admin_message, $user_id ) {
    
    $user_info = get_userdata( $user_id );
    
    // Append new text.
    $admin_message .= __( 'Subscription Name: %subscription_name%', 'rcp' ) . "\n\n";
    
    // Convert email tags.
    return rcp_filter_email_tags( $admin_message, $user_id, $user_info->display_name );
    
}

add_filter( 'rcp_before_admin_email_expired_thanks', 'ag_rcp_before_admin_email_expired_thanks', 10, 2 );