Custom new exchange rate type in billing document

Hello Friends,

We have a business requirement to determine new exchange rate other than the standard 'M' type in exceptional scenarios, and for this the exchange rate also differs for specific custom exchange rate type. Could you please suggest, how this can be fulfilled using the usereixt, any specific userexit availalble. As i understand its not possible in standard.

In Standard default exchange rate type is passing in include LV60AA95

Thanks in advance for your valuable inputs.

Anticipating a positive response.

Best Regards,

Goutham