Supplier Invoice M93 Posting C31 override

Hello,

we are new in iFS world so we would like to ask for help here. For Supplier Invoices we plan to use posting control M93 and control type C31 for automatic account number assignment. Everything is set-up and working properly but there not possibile to override assigned account if neccesary during Manual Invoice processing. "Override” selection doesn’t seems to allow that. Any sugestions how to achieve this except reopening and edditing of line of the PO? Thank you