Braintree links the processing currency with the Merchant Account ID. Therefore, you have to setup for each currency that you want to process the Merchant Account Id.
In case you want to settle in a new currency. You have to create a new new Merchant Account and select the new currency you want to settle in. Inside the application you can then create a new processor configuration for this currencies. It is encouraged to create new connectors for this processors and apply conditions based on the currencies.
Source: braintree documentation