Adjust cost on a single serialized item


We need to be able to adjust the costs on serialized item based on their age. almost like a FA depreciation. I wanted to ask what the best journal is for doing this. It seems like if I use an inventory adjustment or inventory movement, I need to have a quantity line that is a negative count at the current cost and a positive line to bring the item back at the new cost. Am I missing anything and is there a way to just adjust the cost of a serialized item without removing it and bringin it back in?