how to add custom links in single product ?

position: in description, afer add to cart, or anywhere I can insert in product page.
custom link: eternal links I can edit for each product individually.
link element: can be text, image, button.
The key is I can edit stye of this link element globally, the link url is different for each product, but the link element itself must be edited in a overall place, so I don’t need to edit or modify for each product pages.

if this can be done in a simple way , it’s best. if this is complicated and needs extra job, I can pay to finish. please let me know. thanks