shein
Rav Moshe, one of the biggest Ashkenazi posek, says that they should change to Ashkenaz.
If your going to quote Rav Moshe, do so correctly. Don’t be part of the 90% of people who say things in his name which is either untrue or skewed.
What Rav Moshe said was that if you daven Nusach Sefard you can permanently change to Nusach Ashkenaz. However if you daven Nusach Ashkenaz it is assur to permanently switch to Nusach Sefard.