Changing SAP Business One Inventory Valuation Methods in 9.0

We would like to the change Inventory Valuation Method from FIFO to Moving Average. We noticed that in 9.0 we are able to change methods even though there is inventory stock. Is it really changing from FIFO to Moving Average? If so, is it revaluating the current inventory? It doesn't look like it is. Last, will it use moving average only for any new purchased/produced inventory? Please explain how the inventory valuation method change works in 9.0 and the impact on the general ledger inventory accounts.

Thank you,

Wayne