Changing store currency from a plugin Is it possible to change the store currency from a plugin?

I know about COMMERCE_PAYMENT_CURRENCY, but I'm not sure how to set that one early enough.

It also seems like it doesn't affect the displayed price. Do I need to use the commerceCurrency in combination with the cart.paymentCurrency everywhere I display a price?
In your plugin have you tried updating the currency and paymentCurrency fields in the craft_commerce_orders database table?

Depending on when you want to set the currency and how you are determining it, you could either do this by a direct database query, or modify the values in the order model before it is saved using this hook: https://craftcommerce.com/docs/events-reference#commerce_orders.onbeforesaveorder