Why would they bother? The A346 isn't even certified as full freighter yet. It will cost a lot to certify it, the extra length isn't needed for outside parts cargo, it's usually the bulk/height. They can better use some 2nd hand A-300s if they need a few more Beluga's, or use the A-330 as platform for a few new Beluga's.
nobody has ever died from hard work, but why take the risk?