This is already possibly with Amazon but not with Ebay
Currently it takes it from the LW barcode but with Ebay trying to link everyone together more using EANs, we would like to be able to list using a different barcode to the one we use for scanning items out etc.
This will help to stop ebay cross promoting the same items to our listings as well as merging them together (something I assume will eventually happen)
I can confirm that this is planned to be released with the next update to Linnworks.net (v5.118.0)
Head of Implementation
Linn Systems Ltd