Changing Fields Historically on Billing Documents - Sales District

Hi

Is it possible to change fields historically on a billing document ?

I wish to change the sales district (VBRK-BZIRK) on Historic Billing documents.

This is due to an external reporting system we use - Business Objects.

I am able to change the same field on the sales order VBKD-BZIRK, but not on the Billing document

Is there a MASS change program available to use at all ?

Please advise

Many thanks

Tony