Change Myanmar money (FEC) at Yangon International Airport after your arrival in Myanmar is not necessary nowadays. You have to change $200 at the airport into Myanmar money before. It is very much possible but you will certainly have to "help" one of the staff in
Myanmar exchange. This being said, you are given by Myanmar Government FEC worth exactly the same amount as US$ and you can freely spend those with local Myanmar people. Therefore, changing Myanmar money less is recommended only to people who are staying a short period of time and will never spend so much. But now you will not face such difficulties at all in Myanmar. So you are free to make your decision on not to financing Myanmar government by not changing your US dollars at the airport into change Myanmar money.