If you want to assign the proper UI card, then simply replace the existing one with the vanilla card. UI cards take the unit's dictionary tag as name. So, for 'Armoured Hoplites', whose dictionary tag (in EDU) is greek_hoplite_elite, the card file will be greek_hoplite_elite.tga. For the small card, you need #greek_hoplite_elite.tga. export_units.txt only contains the textual info, though it depends on the dictionary tag as well.
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