Impact of changing BFB Billing Cycle from Day 3 to Day 13

Summary: Would like to understand the impact of changing BFB Billing Cycle from Day 3 to Day 13 and whether this will affect old transactions available in the system

Content (required): Currently, as a business process for BFB, we are running BFB job on Day3 and then on Day 15 we have direct debit being enabled and funds will get auto-debited from the customers account, but the business requirement is after Day3, they want to make adjustments and apply credit memos to existing transactions, if we do this with our current business process which is on the day (Day 3) of running BFB the due amount shows lets says 1000, but on the day(Day15) of direct debit it has due amount as 900, as credit memo of 100 being applied in