After CDS data has been created in an environment, you cannot change the currency of the CDS data. If you need to change the currency, you need to delete the environment, recreate it from scratch and pick up the currency you wish.
With data being used and growing, this process may take you a month or 2 to complete, properly!
It may be hard, critical at the back-end to change the currency of the CDS data, but it is not impossible, nothing impossible I guess. I suggest that admins are allowed to change the currency of a CDS data from within the environment CDS settings, at least once.