Quote Currency must match Opportunity Currency if Primary = True on the Quote. If the Products are included in the Opportunity as opportunity line items, the opportunity currency to be unchanged after the primary quote creation. Make sure to set the opportunity currency correctly when creating the opp and the quote. If you find you need to change the currency after quote creation, just uncheck the Primary box in the current primary one, edit the Opp’s currency and create a new primary quote. DO NOT DELETE THE PRIMARY QUOTE as it will not help the currency adjustment. If the Primary Quote is deleted, all of the related Opportunity Products must be deleted before changing the Opportunity currency. To adjust the Opportunity amount, utilize Discount field in Opportunity Product to exclude a Product (Discount = 100%) out of the total Opp amount. Non-primary Quotes can have a different currency but those can never be made Primary for Closed/Won unless it matches Opty Currency.