You know how the pvp armor has only two mods in it? Mods and enhancement, and the armoring is not visible, which is the part that contains expertise.
Just have a green armoring (or just any quality armoring) in your inventory, open the PvP item you want to remove the armoring from, and right-click on the armoring you have in your inventory. The armoring slot should now appear in the modification window. Simply just drag the armoring you added back to your inventory, and the epic armoring should now be visible and can be removed (at a cost of credits of course)
Here is a picture of how it should look: https://i.imgur.com/xhgVL.jpg
Edit:
It seems like it is also mentioned on the official forums
Edit 2: This has been fixed with the 1.0.2d patch, see patch notes. As for barrels/hilts, I don't know if it would still work, has to be confirmed. (They only mention armoring in notes, but hilts/barrels might be of same "type")