Legacy customer no in customer and vendor master records

Hi

We plan to migrate the Customer and Vendor master data to SAP S/4 Hana from legacy systems.

Can we renumber these active Customer and Vendor nos. in SAP number ranges without impacting the open items ( AR / AP/ Invoice/ Sales order) at the time of cut over ?

How will SAP correlate an open item with the new customer nos in SAP ? Or do we need to continue with the legacy numbering for customer / vendor?

Thanks