Fixed variables (exchange rate) to use in a calculation

Is it possible to define some fixed variables that can be used, for example, in the calculation of prices for a product? Since we purchase goods in many different currencies, we want to make all calculations in our supplier’s currency, but sell the product in our currency, NOK. For example, we want to be able to make the calculation in the supplier’s currency and only change the exchange rate in one place for all products that have, for example, $ in the price calculation. I would like to change this when, for example, the exchange rate has increased or decreased by 10%, without having to go into all the products that have that currency in their calculation.