In my view buying and cancelling/ changing is a poor choice which an employer can use against you. Many employers will accept a print out of the cheapest eco fare and allow you to book a higher travel class as long as you pay the difference directly. If you have a corporate TA they can usually do this directly invoicing the y amount to the employer and the additional cost to the employee. This is more transparent and protects you more as the employer is aware of everything from the start. It also means you avoid differences in conditions that could become an issue - for instance if the initial y ticket is more flexible than the J ticket you purchase and you need to change or cancel the trip later: