Not quite sure if this is your looking for, but if it's not, it should at least give you an idea how to get it.
Simply put this in your Stylesheet section:
opacity: 1 !important;
transition: opacity 0.5s 2s ease-in;
The "2s" means a two second delay before the transition, and then the "0.5s" means transition to complete transparancy in half a second.
That will affect all <<linkreplace>> macros in your game.
Unfortunately, you can't use the same trick with <<linkappend>> because it works differently, so you'll have to use <<linkreplace>> instead of that.
Hope that helps! :-)