Change to the Specifications in G/L Accounts 

You can no longer change the tax category (input or output tax account) for a tax account if the account has a balance. For example, you cannot assign another indicator at a later date to a tax account for tax on sales/purchases that contains the indicator > in the Tax category field. In the same way, you cannot subsequently determine that a G/L account, which has a balance, is a tax account. The system prevents such changes from being made.

In all other cases, that is, if the accounts have no balance or you are making changes to accounts that are not tax accounts, nor are they to be used as tax accounts in future, only a warning message is issued.