If you just want to add the size description from a product listed value to the item number, then you can make a simple COD text file and use the ExecuteScript command to concatenate that onto the item number.

Paste this into the COD

If Item.CID=838 Then
	item.number = item.number + "-" + item.description
EndIf

Note: You will have to make sure to avoid the scenario of running this script on something that has already had the size descriptor added.