Changing Account Currency

SBO 8.82 help states under Chart of Accounts Window that If you define a foreign currency account and record transactions for it, you cannot later change the account currency or perform transactions in any currency other than the defined account currency.

But at the end of same help file, there are FAQs and this is mentioned.

Q:Is it possible to change the currency defined for G/L Account or Business Partner after journal entries have been posted?

A:If the currency defined for this G/L account or business partner is either the local currency or a specific foreign currency, it is possible to change it to All Currencies. If the originally specified currency is All Currencies, it is not possible to change it.

These both are contradictory. Can you please tell which statement is correct?