Customize a section of the Admin Activity Email

my_pmpro_modify_admin_activity_email_sections.php

<?php
function my_pmpro_modify_admin_activity_email_sections($email_sections, $frequency, $term, $report_start_date, $report_end_date, $date_range) {
    // Directly check and modify the 'total_members' section if it exists
    if ( isset( $email_sections['total_members'] ) ) {
        $email_sections['total_members'] = '<tr><td>Replace with your custom code to retrive total member data here.</td></tr>';
    }
    
    // Return the modified $email_sections array
    return $email_sections;
}
add_filter('pmpro_admin_activity_email_sections', 'my_pmpro_modify_admin_activity_email_sections', 10, 6);