How to change the standard SettleDatePrinc

I have created an automated payment process with batch processing.
Here the SettleTransaction method of CustTrans is used as a standard process, but in this process the SettleDatePrinc is set to DateOfPayment.
I would like to set DaysDate, how can I implement this?
I want to use the SettleTransaction method because the SettleTransactionPrivate method cannot be extended with a Private method.

Thanks for your help.

I solved it by using the updateOffSetVoucher.