Do you mean when the link is saved, or when it is rendered?
If you want to add things to the LinkCollection when it's rendered, the property is just a collection of LinkItem objects. The collection has methods for Add, Remove, etc. You sbould be able to create a new LinkItem object and insert it at runtime, if you like.
How can i change the values or add values dynamically/programatically for a PropertyLinkCollection property.
Thanks in advance.