If you are selling an eBook in PDF format and using our PDF Stamping feature, then each buyer's original download link will always download the personalized copy from their original purchase. This is explained in the "A few things to keep in mind" section of our help page for PDF Stamping:
You could use your Seller Admin > "Send free download link", to send them a fresh link for the current edition, but that would not engage PDF Stamping since there'd be no actual checkout being performed in that case, so there's no checkout data to send to the Stamper.
To issue a free link that engages the Stamper, we'd recommend creating a secret discount code for yourself that grants 100% off the item total, then use your own Add to Cart button for the product and enter the code in your cart. This will allow you to use our Free Checkout, where you'd simply enter the recipient's name and email address on their behalf, so they will be emailed a link to the thank-you/download page where they can download their copy of the current edition stamped with the name and email you provided during Free Checkout. Doing it this way is just simpler and easier than creating a series of different, single-use discount codes and then sending each person their code with an Add to Cart link to perform a Free Checkout themselves.