Converting Valuated Stock to Non-Valuated Stock?I

Converting Valuated Stock to Non-Valuated Stock?I
I have this situation:Currently,my client stock materials are valuated and it is maintained both quantity and value under each material type.There are open items pertaining to each of these stock materials.Now,one of my client department said that they want to convert each and every stock materials from valuated to non-valuated so that instead it is been store under a special stock account,it will be expense off.I know I need to change in each material type under value on all area to non value on all area.But what impact does it pertain to my client finance or logistics as I notice a lot of reports cannot be use after I change it (in simulation)?