I have a reward flight booked in Business for 60000 miles sometime last year for this july travel. with new miles rules, for same route post feb, it is costing 80000 miles. I want to change the date of travel. I am premier 1K. origination and destination remains same. date and carrier changes based on reward availability. previously it was turkish now it will be lufthansa. will united charge me additional 20000 miles for it?