G/L Class code change on inventory item

I have the item master with g/l class code IN79.  The Branch Plant has IN80 in the g/l class.  We created inventory and consumed it all out of this branch plant.  I moved the g/l class code to IN79 for the branch plant.  When I now create inventory it is still defaulting to IN80.  How can I get the new g/l class code to work on new inventory items?  There are no open sales orders or purchase orders with that item.