Edit fields on Gravity Form

gravity-form-field-populate.php

<?php
/**
 * Change the way a field is rendered in Gravity Forms.
 * 
 * This example shows how you would dynamically create options for a select field.
 * 
 * @author Joshua David Nelson, [email protected]
 * @link 
 */

add_filter( 'gform_pre_render_1', 'gform_currency_field' ); // be sure to change the number "1" to the form ID, this is a dynamic filter

function gform_currency_field( $form ) {
	// find the currency field and add the options
	foreach( $form["fields"] as &$field ) {
		if( $field['type'] === 'select' && strpos( $field['cssClass'], 'currency') !== true ) {

			// The first, "select" option
			$choices = array( array( 'text' => 'Select a Currency', 'value' => ' ' ) );

			$currency_list = $this->currency_options();
			// Check for results
			if ( !empty( $currency_list ) ) {
				foreach ( $currency_list as $key => $value ) {
					// add users to select options
					if( $key == 'USD' ) {
						$choices[] = array(
							'text' => $value,
							'value'  => $key,
							'isSelected' => 1,
						);
					} else {
						$choices[] = array(
							'text' => $value,
							'value'  => $key,
						);
					}
				}
			}

			$field['choices'] = $choices;
			break;
		}
	}

	return $form;
}