Change Requisition / PO distributions accounts based on a descriptive flexfield

Hi, I´m asking for your help, to see how to made changes to a requisition / PO distribution accounts, (using destination type as Inventory)?, once the account has been automatically created, based on a value from a descriptive flexfield (i.e. the descriptive flexfield comes as a list of different elements which is assigned a number, from 1 to 7 (funding sources); and what I´m looking to achieve is to change a segment of the distribution account with the value selected from the flexfield:

Original account created in distributions (field Charge Account):

1-1151801-00000-06-265-152-002-M001-24601-1-4-000