The change fee is charged each time you make a change. So, if you call in today and change the dates for BRU-JFK-LAS and LAS-JFK-BRU, during the same call, then the change fee will be €200 (assuming that both directions are subject to the same change fee). However, if you call in today and change just the BRU-JFK-LAS, and then a few hours later change the LAS-JFK-BRU, then you will be charged €200 each time for each change. The change fee is also per person.

If the new flights cost €100 more, your overall change will be €300 per person, meaning you will pay €600. But if the new change is €100 cheaper, then you will only pay €100 per person, meaning €200 total. Similarly, if the new flights are €300 cheaper, you will get back €100 per person. But this will only be returned to you in the form of a voucher you can use later.