Hello Andre,
I have same field but my current environment is like following:
AX runs with 3 companies and they all have the same ItemId.
Also my ItemId equals to my Product number in EcoResProduct table.
When I import barcodes for a Product, I just get the Product ID for DisplayProductNumber
When I do it for a Product Master, I generate the DisplayProductNumber with merging color,size,style, configuration and Product ID like I wrote in the query below.
My last import looked like following:

And my SQL query is:
SELECT
distinct
barcodeSetupId
,max(itembarcode) as ItemBarcode
,UnitId
,'No' Blocked
,[Description]
,'No' [RetailShowForItem]
,'No' [useForInput]
,'No' [useForPrinting]
--Display Product Number Structure: 000106 : CONFIG : SIZE : COLOR : STYLE
--Use for [EcoresProductDimensionGroup_Name]=0013
,[Itemid]+' : '+[inventconfigid]+' : : : '+[inventstyleid] as [DisplayProductNumber]
-- Use for [EcoresProductDimensionGroup_Name]=0005
--,[Itemid]+' : '+[inventconfigid]+' : '+[inventsizeid]+' : '+[inventcolorid]+' : '+[inventstyleid] as [DisplayProductNumber]
--Use for [EcoresProductDimensionGroup_Name]=0010
--,[Itemid]+' : : : '+[inventstyleid]+' :' as [DisplayProductNumber]
--Use for [EcoresProductDimensionGroup_Name]=0012
--,[Itemid]+' : '+[inventconfigid]+' : : '+[inventcolorid]+' : '+[inventstyleid] as [DisplayProductNumber]
--Use for [EcoresProductDimensionGroup_Name] =''
--,[Itemid] as [DisplayProductNumber]
FROM
[AXMasterData].[dbo].[PRODUCTMASTERDATA]
group by itemid,InventColorId,InventConfigId,InventStyleId,InventSizeId,
barcodeSetupId,UnitId,Description
One thing I noticed, Barcode entity does not let you import more than 1 barcode per Product ID, I found that kind of weird. Also for this reason I had to pick the Max ItemBarcode in my query for initial import.