Guild Wars 2

So I transmuted this skin onto a Rabid exotic backpiece. Can I upgrade this in the MF? for the defensive infusion slot? If I do will it go back to apothecary stats?

No you can’t.
the capacity to upgrade is in the stats and not the skin. So if you transmutated the stats to a different back piece it is basicly that back piece but with different looks. So it is as upgradable as the item with the orignal stats