Age of Empires 3
The in-game cheats are a bit cumbersome to use but are effective. To take some of the pain out of typing them, I type one, copy it (Crtl+C), press enter to use it then use paste (Crtl+V) until you are done with it.
Alternatively (or in addition), you could edit the XML files that govern the units stats. Use the XML Editor from Microsoft to make changes with ease (but back up the files first).
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