I did resolve this issue, it was simple, you just have to set the field to your own option while duplicating the product.
In my case I had to clear two fields, (Description and SKU) and I just added the following code whenever the on click function on duplicate button was called.
public function duplicate()
{
$this->getWebsiteIds();
$this->getCategoryIds();
$newProduct = Mage::getModel('catalog/product')->setData($this->getData())
->setIsDuplicate(true)
->setSku(null)
->setId(null)
->setDescription(null)
->setShortDescription(null)
->setStoreId(Mage::app()->getStore()->getId());
Mage::dispatchEvent(
'catalog_model_product_duplicate',
array('current_product' => $this, 'new_product' => $newProduct)
);
And in your case you can call the appropriate function may be ->setGShopping($YourString) accordingly.
I hope this may solve your issue.