WooCommerce Product Import Customisation and Custom Field

We have a client that has an product XML feed to populate their products on the store. The simple and variable products all imported fine, but the client replaced the unique product SKU with their own. Now when we import prices again from the XML feed - they do not update as we are matching product SKU and Price - with their SKU - products cannot match. So we need to have an extra additional field in woo commerce for simple and variable products that records the manufacturer SKU code and allows them to retain and display the manufacturer SKU to admin only. Below is an example of the XML feed : <Product> <ItemCode>PEN-1258-BU</ItemCode> <Name>Atom Pen & Highlighter</Name> <Description>A fun 2-in-1 pen that will be appreciated by its recipient. Ball pen on one side and highlighter on the other. Highlighters available in 2 awesome colours • Pen has black German ink.</Description> <Price>5.14</Price> <Flags>0</Flags> <BaseItemCode>PEN-1258</BaseItemCode> <Id>4a5d31f8-b238-4666-b68d-6d0a6974fdef</Id> <Size /> <Colour>BU</Colour> <Promotion>0</Promotion> <ColourName>Blue</ColourName> <StockCheckCode>PEN-1258-BU</StockCheckCode> </Product> <Product> <ItemCode>PEN-1258-Y</ItemCode> <Name>Atom Pen & Highlighter</Name> <Description>A fun 2-in-1 pen that will be appreciated by its recipient. Ball pen on one side and highlighter on the other. Highlighters available in 2 awesome colours • Pen has black German ink.</Description> <Price>5.14</Price> <Flags>0</Flags> <BaseItemCode>PEN-1258</BaseItemCode> <Id>4a5d31f8-b238-4666-b68d-6d0a6974fdef</Id> <Size /> <Colour>Y</Colour> <Promotion>0</Promotion> <ColourName>Yellow</ColourName> <StockCheckCode>PEN-1258-Y</StockCheckCode> </Product> As you can see ITEMCODE is unique and this is the element client has changed. So now we need to try and update existing records to bring in the Manufacturer ITEMCODE as an invisible field for all products so we can match to it on al future imports. So the woo commerce administrator need to see the imported manufacturer code and need to have their SKU code on the actual order. They do not want the public to see the manufacturer code as it can be searched and user can purchase direct from source in some cases. So we need to have two SKUs - One visible to public and one not visible. ( nly to admin)