In 4.6x, you can assign valuation class to Material Group.
It is useful in the sense that user do not have to manually do an Account Assignments.
For stock items, valuation class cannot be changed whenever the stock on hand is not zero.
Valuation class are tied to a G/L account.
A change of valuation class means a change of G/L account.
In FI concept, you have to debit and credit to balance the G/L account. That is why your stock must be zero before the system allows you to changed the valuation class. If it is not zero, you have to either transfer it to another material or do a dummy issues. After changing the valuation class, do a reversal entries for the stocks which you have transfer out or you have done a dummy issues.
IMG – Material Management -> Purchasing -> Material Master -> Entry aids for items without a Material Maste
Valuation Class for Material Group without Material Master