Don't worry. When you have done it and the first fire-forming load has been fired, they will perform just as well as any other when they are reloaded. Maybe even better than the correct cases on their first firing - because they have been formed to fit your rifle. Something that the correct cases also require, because of the manufacturers' habit of making new cases to SAAMI/CIP minimum dimensions minus a manufacturing allowance = undersize!
BTW, can someone explain why brass (apparently) cannot be exported from the USA.