Card Hack For Skirmish Mode:

Locate the sp_NameOfCity_homcity.xml file in your ...Age of Empires 3savegame directory. Edit or open the file using Notepad or a similar text editor. In the file, search for the text similar to the string and you should find a list of all the cards available for the game.

Place the technology card you want in between the and section and you should be able to play any of the cards you want. Save the XML file and boot the game. Note that normal game restrictions of having only eleven cards is still in effect.