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it should be quite simple to go from Engineering to L&S. Not the other way around.
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It would be a lot simpler to double major in CS and humanities, for L&S. If you wanted to do the Engineering / Humanties L&S route, you would have to satisfy requirements for both schools separately, called getting simultaneous degrees. The net effect of this is probably 3-6 extra classes than a double major. However, do note that The College of Engineering will not accept simultaneous degree applications for EECS (unless you are in MET).