More modding questions from Spartan198!

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.

I found the XGM greek_hoplite_elite.tga file in the UI folder, but vanilla RTW doesn't seem to have a UI folder.

Vanilla UI folder is packed away in a .pak file, look into your data/packs folder. Use Verc's .pak extractor to get the files out and then do whatever you want to them. Link for the tool can be found in the tools thread of the Scriptorium iirc.