Default Exchange Rate Type

Dear All,

If we do not assign any exchange rate type to any document type or customer / vendor master data, the system picks the default 'M' exchange rate type. Can anyone let me know where this default setting has been made and whether this setting can be changed? What if I do not maintain exchange rates for 'M' instead I do it for 'M1'

I have a scenario, wherein I want to make exchange rate type other than 'M' as default and we do not want to make it at the document type level or customer / vendor master data level.

To make things more clear, this is not related to the realignment / foreign currency valuation. This is related to recording of invoice export / import or credit / debit notes..

Can anyone let me know how would this be possible?

Full points guaranted