Invoice Payables options in r12

Hi

Can someone please help me with the invoice payables option.

1) Allow Remit to Account Override: If my understanding is correct does it allows to change the account at invoice header level. I tried but an error message popped. Error Message: Bank Account at invoice header level is used for one time defaulting to payment schedule, any subsequent update of bank account at header level will not overwrite the bank account information in schedule payments.

2) Allow Remit to supplier override: what does this mean ?

3) Allow adjustment to paid invoices: does it work only for PO matched invoice because I tried with standard invoice and after paying it I was not able to make any changes to the distributions.