The order currency is initialized with the customer currency. Once the order is created, this information is no longer modifiable. If however the currency is modified after having entered the order lines, but before creating the invoice, then a conversion of the prices and discounts will be carried out. it is however possible to carryout a new price list search as function of the new currency by responding Yesto the question "Do you want to recalculate the prices and discounts ?".