I’ve seen people err on this so often that I thought it was worth noting: If you’re rearranging citations in a footnote (usually to follow the Bluebook citation order recommendations), make sure you look closely at the parentheticals.
Some parentheticals in a long citation refer back to earlier parentheticals, using phrases such as “(same)” or “(similar except for …).” Such references make sense, because they make string citations shorter and, often, easier to grasp. But if you just rearrange the order of the citations without updating the parentheticals, the parentheticals will now no longer be correct.
More broadly, some citations in a citation string are not in the same order as the Bluebook recommends, precisely because they break down sources by subject matter — for instance, they might cite some statutes that use one phrasing, with “same” or “similar” in all the parentheticals but the first, and then some other statutes that use another phrasing, with “same” or “similar” in all the parentheticals but the first. Watch for that; and if you see that, then either don’t reorder the citations in a way that will break this useful separation, or at least talk to the author about whether he wants to keep his original citation order.