Yes. No.
Well, sort of. You know about objStatus "hidden", right? Well just put the link in an objective which is hidden at the start of the mission and revealed at the appropriate moment. I know it's not ideal. Phrase the objective wording so that you can tick it straight away. For example
Access secret files
with the link embedded in the text. I haven't been able to think of any other way of hiding and revealing stuff. Don't forget that you can hide an existing objective at the same time as revealing another, so that it appears one replaces the other.