Be kindly informed that there will be no problem if you change your arrival airport. Since the visa approval letter works at three International Airports of Vietnam:
- Noi Bai International Airport in Hanoi
- Tan Son Nhat International Airport in Ho Chi Minh City
- Danang Airport in Danang City
You still get the visa stamped onto your passport at any of these three airport regardless of which you put in your visa application.