Data Import or Rename Tool - Importing Legacy Purchase Orders

We are setting up erpNext v12 / cloud hosted and want to import existing (old) purchase orders from our previous system. I want to keep the existing numbers. Is there any way I can import the Purchase Orders and manually set the series number? I have tried the import tool and the renaming tool.
When we first set up erpNext we started the series number above where our old values were so I want to put the numbers below the current naming series.
current PO-0562
legacy PO-0200 to PO-0400


If you have DB access, you could potentially edit the data directly in the tabSeries table, but it is a high risk method that is not advised unless you are very experienced with SQL

The easy way out? Create a custom field in the Purchase Order form add the older numbers there. This way you can keep a reference for old numbers easily without much hassle. You can create a new naming series to differentiate between legacy imports.