Deleting Old Invoices
You will need to know what accounting basis you are working on, Cash or Accrual.
If you are working on an Accrual accounting basis:
If the invoice is dated in a previous BAS period, create a new invoice as a credit note (using the original dissection amounts) in the current BAS period. Both the invoices can then be "paid" through Cashbook (Total of the transaction will be zero so the bank account used is irrelevant).
If the invoice was/is dated in the current BAS period, delete as for Cash below.
If you are working on a Cash accounting basis: