Example of using the pmpro_confirmation_url filter to change the PMPro confirmation page for new users.

my_pmpro_confirmation_url.php

function my_pmpro_confirmation_url($url, $user_id, $level) {
	$already_member = get_user_meta($user_id, 'already_member', true);
  if(!$already_member) {
    update_user_meta($user_id, 'already_member', 1);
    $url = home_url('/my-dashboard');
  }
  
  return $url;
}
add_filter('pmpro_confirmation_url', 'my_pmpro_confirmation_url');