after CDS data has been created in an enviroment, you cannot change the currency of the CDS data. If you need to change the currency, you need ot delete the enviroment, recreate it from scratch and pick up the currency you wish.
With data being used and grawing, this process may take you a month or 2 to complete, properly!
It may be hard, crticial at the backend to change the currency of the CDS data, but it is not impssible, nothing impossible I guess. I sugest that admins are allowed to change the currency of a CDS data from within the enviroment CDS settings, at least once.