Its only possible to set FIFO on items of type Service and Non-Stock. Often these Items are not bought so there is no purchase done on the Items. It should be possible to change Cost price on the Items as cost price can change over time but its not possible to change this manually as it should be when Item is FIFO.

As it is now the initial price set on the Item will never change (and cannot be changed) except when doing a purchase which is often not done on these types of Items. Either it should be possible to choose other than FIFO or change cost price manually when Item is Service and Non-stock.