If you enter worldbuilder during your game, you can make a lot of edits to your game without even editing your save files. In city editor, you can change your amount of gold, and you can change terrain and place units anywhere on the map. Once you're done, just close the worldbuilder (you don't need to save anything), and the changes will be made to your civ. I'm sure there are a lot of other things you can do, as well.
Hope that helps.
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