No. You can allow more than one color to be human in the editor. However, when you enter the game, the options screen for custom campaigns is the same as for regular campaigns. It does not allow you to pick your color or set more than one player as human.
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My guess is that it wouldn't be balanced. Whoever won the first game would have an advantage in the second and an even bigger advantage in the third, and so on. Once one player fell behind in hero development, it'd be very difficult to catch up.
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