After integrating D365 Sales and D365 Finance and Operations with Dual write, you can no longer change the currency of Sales Orders in FnO, due to the field being locked in D365 Sales.

Dual Write integration thus removes existing functionalities from FnO and limits business processes. It should be possible to edit the currency field for Sales Orders in D365 Sales for better integration of D365FnO and D365 Sales with Dual Write.