Hi,
1. Sure. You can create a custom field of the table "product" via the menu Display>Custom fields with the Essential or Business edition and then that link can be displayed automatically on the product page if you turn on the frontend display option of the field and enter the external URL in the custom field.
2. You can edit the file "listing_img_title" of the "product" view via the menu Display>Views for that. You can change the code:
<a href="<?php echo $link;?>">
<?php }
echo $this->row->product_name;
to:
<a href="<?php echo $this->row->FIELD;?>">
<?php }
echo $this->row->product_name;
where FIELD is to be replaced with the column name of your custom field.