Valuation class in the material master in SAP

Can we change the valuation class in the material master once it is assigned?
Once a material is assigned to a valuation class in the material master record, we can change it only if the stocks for that material are nil. If the stock exists for that material, then we cannot change the valuation class. In such a case, if the stock exists, we have to transfer the stocks or issue the stocks and make the stock nil for the  specific valuation class. Then only we will be able to change the valuation class.