Setting up Accounting looks the same for every team. The books start in the team currency, and you can choose another right there.
If the team has not chosen a currency, the one you pick becomes the team currency. If it already has one, it stays as it is and only the books use the new one.
The team currency no longer locks once the books are set up. It sets where new invoices, expenses and rates start, and the books keep the currency they were set up in.