To do that you'll have to edit the "form" file of the "product" view of your back-end template through the page "
Code:
if(!empty($this->fields)){?>
<table class="admintable table" width="100%">
<?php foreach($this->fields as $fieldName => $oneExtraField){
if(!$oneExtraField->field_backend){
if($oneExtraField->field_type != "customtext"){?>
<tr><td><input type="hidden" name="data[product][<?php echo $fieldName; ?>]" value="<?php echo $this->element->$fieldName; ?>" /></td></tr>
<?php }
}else{ ?>
<tr id="hikashop_product_<?php echo $fieldName; ?>">
<td class="key">
<?php echo $this->fieldsClass->getFieldName($oneExtraField);?>
</td>
<td>
<?php
if(!isset($this->element->$fieldName))
$this->element->$fieldName = $oneExtraField->field_default;
?>
<?php $onWhat='onchange'; if($oneExtraField->field_type=='radio') $onWhat='onclick'; ?>
<?php echo $this->fieldsClass->display($oneExtraField,$this->element->$fieldName,'data[product]['.$fieldName.']',false,' '.$onWhat.'="hikashopToggleFields(this.value,\''.$fieldName.'\',\'product\',0);"'); ?>
</td>
</tr>
<?php }
} ?>
</table>
<?php }
