shows how to change the display of a Participants Database field

change_currency_value_display.php

<?php
/**
 * Plugin Name: PDB Customize Currency Display
 * Description: replaces a zero value with a custom string
 */
add_filter( 'pdb-before_display_form_element', 'xnau_show_currency_value', 10, 2 );
/**
 * replaces a 0 value with a string
 *
 * @param string $display the display string
 * @param object $field the field object
 *
 * @return string the string to display
 */
function xnau_show_currency_value( $display, $field )
{
  if ( $field->name === 'my_currency_field_name' ) {
    if ( intval( $field->value ) === 0 ) {
      $display = 'Call';
    }
  }
  return $display;
}