The caravan merchant that shows up on the overview map every once in a while offers the ability to swap artifacts. so you can change artifacts of non-elven type for elven artifacts.
Thanks for the info, I have discovered this from a recent update, and had pleny of artifacts (esp. noble artifacts) to swap out. I now have my forces up to level 10 at the Command Centre, which I believe is the current maximum. It also helped for magic artifacts that some Squad leaders needed to max out, so cheers for that again.