This article should explain link restriction: Link
You can't change the name of a link. What I do to get around this is I make two identical links, one that's visible before the player has triggered the condition and vanishes once they do, and one that's invisible until they trigger it.
To change the words on a page depending on variables, you can use $PAGETEXT commands, as explained in this article: Link
This article may also help you with changing words on the page: Link