frm_get_paged_fields

This code will get all the specified fields and display them on the last page of the form. These fields will still appear in their normal position as well.

add_filter('frm_get_paged_fields', 'get_extra_form_fields', 10, 3);
function get_extra_form_fields($fields, $form_id, $error=false){
  if($form_id == 25){ //change 25 to the id of the form to change
      $prev_page = FrmAppHelper::get_param('frm_page_order_'. $form_id, false);
      if($prev_page > 3){ //change 3 to a number higher than the order of second to last page break
          $new_fields = FrmField::getAll("fi.id in (45,46)"); //change 45,46 to the IDs of the fields you'd like to show on the last page
          $fields = array_merge($fields, $new_fields); //if you want to mess with the order, you can tinker with this on your own
      }
  }
  return $fields;
}

The $prev_page > 3 is a bit confusing. In my example, I had a page break that was the 5th field in the form, so pick a number smaller than that, but bigger than any previous page breaks.

Use this if you would like your form to all be one a single page when you are creating or editing an entry from the back-end.

add_filter( 'frm_get_paged_fields', 'remove_my_breaks', 9, 2 );
function remove_my_breaks( $fields, $form_id ) {
  if ( ! is_admin() ) {
    return $fields;
  }
  if ( $form_id == 12 ) { // change 12 to the ID of your form
    remove_filter( 'frm_get_paged_fields', 'FrmProFieldsHelper::get_form_fields', 10, 3 );
    foreach( (array) $fields as $k => $f ) {
      if ( $f->type == 'break' ) {
        unset( $fields[ $k ] );
      }
    }
  }
  return $fields;
}

If you want to remove page breaks on the front-end, remove the following from the above example:

if ( ! is_admin() ) {
    return $fields;
}