I found this tip on the LOTRO forums and tried it. It works! I did it on several of my items. Of course, you must be careful when you do it.
The devs have changed the stats (notably armour value in the latest update) on some gear. For example, if you make the teal medium helm that uses the Ithilgalad Crafting Components today, the crit item level 422 helm will have 28906 armour. Previously, the same helm with the same item level had 24102 armour. The recipe result changed, but old items were not updated. The same thing happened to embers gear from coffers.
There is a trick to update your item to the new stats. If you sell the item at a vendor and immediately buy it back, the stats are updated. It doesn't change the item level, but it apparently plugs in the current stats.
Needless to say, you must be careful that you don't permanently lose the item. If you were to logoff or get disconnected or sell too many other items before you tried to buy it back, you would not be able to buy it back.