I think we used to call it “uping” an item in D2, anyways of the empowered items that exist, can we take a normal epic and upgrade it?
There is not, at least to my knowledge.
You can add component’s and augments to give gear them certain stats/abilities. And each blacksmith has their own special crafting buff that can make crafted gear slightly better than gear that drops. But no way to reroll or upgrade gear.
However I personally anticipate them adding some type of affix re-roll crafting system in the xpac, perhaps behind something like mining?
would be nice, i have an ammy i really want an empowered version of, been hunting forever for that one, would love to empower it 
Ah I see! You mean upgrading between epic items and their empowered versions, not just upgrading/rerolling an item. That would be super cool:D
You can’t do what you’re asking in the OP, but that would be a nice idea for the expansion or as a future feature, since it would add another thing to craft.
It would be a sink for the many components that don’t have a use once you’ve crafted your main items such as helm and relic slots, since you have more options to craft.
Another logical future step could be to add empowered Legendary items, which would mean the current top-end items could stay competitive with a(n assumed) increased item level cap, and Crate could add empowered versions of items that are currently not so good.
That way they could give less popular items a chance to shine, too.